From the Gospel of John, chap 3:25-26 (Revised English Bible)     - - the apostle John has just stated in the preceding sentences that Jesus and his disciples were engaged in the act of baptizing as was John the Baptizer.

25John's disciples were engaged in a debate with some Jews about purification;26so they came to John and said, 'Rabbi, there was a man with you on the other side of the Jordan, to whom you bore your witness. Now he is baptizing, and everyone is flocking to him.'