“And they asked him, and said unto him, Why baptizest thou then, if thou be not that Christ, nor Elias, neither that prophet?”
King James Version (KJV)
1:25 They asked him, Why baptizest thou then? - Without any commission from the sanhedrim? And not only heathens (who were always baptized before they were admitted to circumcision) but Jews also?
Joh 1:25 Why baptizest thou then? If he were Christ, or Elijah, or "that prophet", they could understand why he should establish a new religious rite, but if none of these, why should he do so? Their perplexity shows that the baptismal rite was new to them. There is no proof that Jewish proselyte baptism of Gentile converts existed at this period, save the assertion of the Talmud, written two or three centuries after this. Josephus, who wrote in the time of the apostles, is silent about it.