“When the festival was first celebrated in the Christian church is not known, but it was mentioned in a work from the Eastern church, the *Epistola Apostolorum*, in the 2nd century. In the 3rd century it was mentioned by **Origen**, theologian and head of the catechetical school in Alexandria, and by **Tertullian**, Christian priest and writer of Carthage.” This establishes that by the 2nd–3rd centuries major Christian writers were already mentioning Pentecost as a Christian festival.

Tertullian describes a distinct Christian festive period tied to Pentecost: "In the same way [we celebrate] also in the days of the Passover, in which, not only is it not fitting to bow the knee, but every service is due to joy... Similarly, too, in the period of Pentecost; which period we distinguish by the same solemnity of exultation." He clearly speaks of a "period of Pentecost" that Christians "distinguish" by joyful observance.

In arguing about Christian customs and feast days, Tertullian writes: "We count fasting or kneeling in worship on the Lord's day to be unlawful. We rejoice in the same privilege also from Easter to Whitsunday." In many English translations "Whitsunday" is used for Pentecost, indicating that Tertullian refers to the paschal season from Easter to Pentecost as a time of Christian rejoicing.

“The Solemnity of Pentecost is celebrated fifty days after Easter. It is the feast on which we remember the gift of the Holy Spirit that overturns the confusion of Babel and renews the face of the earth. During the first half of the **3rd century, Tertullian and Origen were already speaking of Pentecost as a Feast that followed the Ascension**. As the pilgrim Egeria attests, Pentecost was a Feast that was already celebrated in Jerusalem in the 4th century.” This Vatican summary explicitly states that Tertullian and Origen in the early 200s refer to Pentecost as an established feast.

The CCEL edition of Tertullian’s "On Prayer" gives the same testimony: "In the same way, too, in the days of the Passover, in which, not only is it not fitting to bow the knee, but every service is due to joy... Similarly, too, in the period of Pentecost; which period we distinguish by the same solemnity of exultation." CCEL notes this as part of Tertullian’s discussion of Christian customs, indicating that Pentecost was observed as a distinctive joyful season.

In "The Chaplet" Tertullian contrasts Christian practice with military customs and says: "We consider it unlawful to fast, or to kneel in prayer, on the Lord’s Day. We enjoy the same immunity from Easter day to Whitsunday." Here CCEL’s English text interprets Tertullian’s Latin as referring to the interval from Easter to Pentecost (Whitsunday), implying that Christians treated this whole period, ending with Pentecost, as a special festive season.

In a section preserving a fragment about Irenaeus, the NPNF translation recounts: "Now this custom took its rise from apostolic times, as the blessed Irenæus, the martyr and bishop of Lyons, declares in his treatise On the Pascha, in which he also mentions Pentecost; upon which feast we do not bend the knee, because it is of equal signification with the Lord’s day, for the reason already alleged concerning it." This shows a later canonical writer citing Irenaeus’ lost treatise as evidence that Pentecost was observed as a feast with specific practices.

Discussing how Pentecost became a Christian feast, the article notes: “Pentecost… commemorates the descent of the Holy Spirit… While the exact date of the first Christian observance is unknown, **by the 2nd and 3rd centuries writers such as Origen and Tertullian refer to Pentecost in ways that suggest it was already celebrated as a distinct feast in the Christian calendar**.” This secondary source summarizes the scholarly view that these Church Fathers document an ongoing Pentecost celebration.

Bishop and martyr Irenaeus says in his treatise On Easter that he also mentions Pentecost, and that on that feast Christians do not kneel. The fragment explains that this custom "took its rise from apostolic times" and specifically connects Pentecost with an established Christian liturgical practice.

A historical-theological note on early practice states: “When **Tertullian** and others refer to Pentecost, they always mean the Easter fiftieth day celebrated as a single feast day.” It further explains that by the 3rd century, “Pentecost had become firmly associated with the fiftieth day after Easter and was treated as one continuous festal period.” This shows that Tertullian’s mentions of Pentecost are understood as references to an established Christian feast in his time.

Analyzing Tertullian’s liturgical remarks, the article summarizes: “Tertullian’s book, On Prayer [**De Oratione Liber**], describes how North Africans kneel when praying on the Sabbath. The kneeling posture is considered a form of humility that must be observed on the Sabbath, **but kneeling during the Resurrection and Pentecost services is unnecessary**.” It adds that these comments occur in a discussion of regular Christian observances, implying that distinct ‘Resurrection’ and ‘Pentecost’ services were recognized occasions in Tertullian’s North African context.

Britannica identifies Irenaeus as an early Christian writer active around 180 and notes that his work *Against Heresies* survives from that period. It also discusses the late-second-century dispute over Easter observance, showing that Christians were already debating feast-day practice in Irenaeus's era.

Pope Benedict XVI quotes Irenaeus and states that "prior to him St Irenaeus had already formulated a truth" about the Church and the Spirit. While this is not a direct historical citation of Pentecost observance, it shows that the Vatican treats Irenaeus as an early witness in Pentecost-related theology and liturgical tradition.

In *De Corona* 3, Tertullian lists Christian festival days as known and accepted: “We count fasting or kneeling in worship on the Lord’s day to be unlawful. We rejoice in the same privilege also **from Easter day to that of Pentecost**.” He cites this as an example of “tradition” observed by the churches. The passage assumes a recognized festal period culminating in Pentecost, indicating that Pentecost was already part of the Christian liturgical cycle in his time.

In this passage attributed to Irenaeus, the text discusses the Holy Spirit and the Church in a way later used in Pentecost liturgy and theology. It does not by itself prove annual Pentecost celebration, but it is a primary patristic text linked to Pentecost themes.

Tertullian is a major early witness for Christian practice in the late second and early third centuries. In these writings he discusses fasts, prayer, and liturgical seasons, providing contextual evidence for the existence of an organized Christian festival calendar in his era, though this page does not directly quote Pentecost observance in the snippet shown.

Britannica identifies Tertullian as an early Christian author from Carthage active around the turn of the third century. This supports the claim's timeframe by placing Tertullian near circa 200 AD, when early Christian liturgical practice was being described in writing.

The site summarizes Irenaeus’s surviving works, especially *Against Heresies* and the fragmentary *Demonstration of the Apostolic Preaching*. While these writings discuss the Holy Spirit’s outpouring in Acts 2, there is **no explicit reference cited here to a liturgical celebration of Pentecost as a recurring Christian feast**. The bibliography and quotations show Irenaeus connecting the Spirit’s descent to salvation history, but not clearly describing a church festival named Pentecost.

The article surveys second- and third-century writers about the Holy Spirit and notes: "Irenaeus’ magnum opus Against Heresies also bears witness to the wide range of spiritual gifts on display within the second century church… Irenaeus openly confessed that the Spirit imparted charismatic gifts to his Church." It then turns to Tertullian: "Another useful passage in his Against Marcion is recorded in 5:8. Here Tertullian does much the same as Irenaeus in laying a hold of the spiritual gifts to show that his Church was really the true Church of Christ." Although focused on charismata, this secondary source confirms that both Irenaeus and Tertullian discuss ongoing post-Pentecost work of the Spirit in the church.

In *Against Heresies* III.17–18, Irenaeus comments on Acts 2 and the Spirit’s coming: he writes that the apostles “were filled with the Holy Spirit, who had been promised by the prophets,” and links this event to the fulfillment of the new covenant. However, **the passage treats Pentecost primarily as the historical day of the Spirit’s descent**, not as a recurring liturgical feast; it does not describe Christians in his time holding an annual Pentecost celebration.

The article notes that Irenaeus's writings are an important window into second-century Christian practice and discusses his role in disputes over Easter dating. It places Irenaeus in the same general period as the claim's "around 200 AD" timeframe.

Tertullian's work is part of the Ante-Nicene Fathers corpus and documents early Christian disputes and customs. It is relevant as a primary patristic source for the period, but the visible text here does not directly mention Pentecost celebration in the extracted passage.

The page states that the Feast of Holy Pentecost "is celebrated each year on the fiftieth day after the Great and Holy Feast of Pascha" and describes liturgical practices attached to the feast. This is modern evidence for the continuity of Pentecost observance in Christian tradition, not direct evidence from the second century.

This article recounts Eusebius's report that bishops in Asia kept Easter on Passover and that Irenaeus argued for peace over the dispute. It is evidence that late-second-century Christians were observing and debating major feast days, including Easter/Pascha, in Irenaeus's time.

The blog compiles patristic quotations, including Irenaeus: "Now this custom took its rise from apostolic times, as the blessed Irenaeus, the martyr and bishop of Lyons, declares in his treatise On Easter, in which he makes mention of Pentecost also; upon which [feast] we do not bend the knee, because it is of equal significance with the Lord's day, for the reason already alleged concerning it." It also cites Tertullian, On Prayer 23: "Similarly, too, in the period of Pentecost; which period we distinguish by the same solemnity of exultation." And Tertullian, The Chaplet 3: "We rejoice in the same privilege also from Easter to Whitsunday." These excerpts are presented as evidence that early Church Fathers recognized Pentecost as a Christian feast period.

This discussion says Pentecost is not an invention of later Christianity and treats it as part of longstanding church tradition. It is secondary interpretive material, useful for context but not a primary historical source.

This overview article introduces major ante-Nicene figures and situates their dates: "Irenaeus (c. 130–c. 200)" and "Tertullian (c. 160–c. 220)." The author explains that these writers provide key evidence about second- and early third-century Christian belief and practice, including liturgical customs such as feasts and fasts, because their works describe how Christians of their time observed the church year.

This page says the excerpt is from a second-century Church Father, Irenaeus, and that it is read on Pentecost in the Roman liturgy. The cited passage from *Against Heresies* discusses the Holy Spirit's coming at Pentecost, which shows Pentecost was a meaningful feast in the tradition associated with Irenaeus.

A popular-level historical overview claims: “**Historical texts from the 2nd and 3rd centuries, writings of Origen and Tertullian, document early Christian celebrations of Pentecost.**” It continues by stating that these writings show “Pentecost was observed as a special feast in the early church, connected to the outpouring of the Holy Spirit and often associated with baptism.” This source asserts that such Church Fathers explicitly document the continuation of Pentecost celebrations.

Eusebius and later patristic collections preserve references indicating that Pentecost was treated as a feast in early Christianity, and patristic editors often note that Irenaeus mentioned Pentecost among observances in his treatise On Easter. This is contextual background rather than a directly verifiable citation from the provided search results.

A parish-level biographical sketch states: “Tertullian (150–225)… was a prolific writer whose works shed light on early Christian worship. His references to **Easter, Pentecost, and other feasts** show that by the early 3rd century the Church already marked these events in a regular way, even if the details of the liturgy were still developing.” While not a scholarly monograph, this reflects the common understanding that Tertullian’s writings attest to the existence of feasts such as Pentecost in his day.

The commemorative entry identifies Irenaeus as a second-century Church Father and dates his death to about 200 AD. It supports the chronological setting of the claim, though it does not itself prove that Pentecost was celebrated then.

The video states that Irenaeus was a second-century bishop and that *Against Heresies* was written sometime between AD 182 and 186. It is a secondary presentation of the chronology relevant to the claim, but it does not directly document Pentecost observance.

The post says Irenaeus was born around AD 130 and died around AD 200, placing him in the time period relevant to the claim. It is only weak contextual evidence and does not directly attest to Pentecost celebration.