John 3:5

Jesus is speaking to a Jewish leader named Nicodemus who has begun to accept Jesus’ authority to speak on behalf of God. When Jesus says that one must be “born anew” or “born from above” to see the kingdom of God, Nicodemus asks how one can be “born again.” Jesus answers him with this unmistakable reference to baptism.

This reference becomes clearer in the context of the passage, since Jesus and his disciples go and baptize people after this encounter. The Church Fathers unanimously agreed this verse referred to baptismal regeneration.