In the following, we have another admission from a critic of baptismal regeneration (here, Richard Bauckham) who admits that the earliest post-NT Christians explicitly affirmed baptismal regeneration:
Since baptism was the rite of
admission to the new community of life it was easy to set it as including in
its symbolism the divine act of giving new life to believers. So it is not
surprising that John 3:5, which undoubtedly refers to that divine act, seems, like
1 Peter 1:3, 23 and Titus 3:5-6, to have been universally understood as
referring to baptism in the early centuries, from Justin Martyr (1 Apol.
61.3-5), Irenaeus (Dem. 41), and Clement of Alexandria (Eclog. 7-8)
onwards (many examples in Ferguson [Baptism in the Early Church,
Eerdmans] 2009). These three New Testament texts were often associated in
discussions of baptism. In this light we might say that John 3:5 was open to a
baptismal reading, which we could understand as the sensus plenior, properly
discerned in the church’s reception of the text. (Richard Bauckham, “Sacraments
and the Gospel of John,” in The Oxford Handbook of Sacramental Theology,
ed. Hans Boersma and Matthew Levering [Oxford: Oxford University Press, 2015], 89)