John 3:25-26

Then there arose a question Or a dispute; between some of John's disciples and the Jews Or rather, a certain Jew: for, “though the common editions read Jews, the greater number of MSS., among which are some of the most valuable, some ancient expositors also, and critics read, a Jew, in the singular; with which agrees both the Syriac versions. To which may be added some of our best modern critics, as Grotius, Cocceius, Hammond, Mill, and Wetstein.” Campbell. About purifying That is, as appears from the sequel, about baptisms, and other legal ablutions. The Jews called all sorts of ablutions, prescribed by their teachers, purifications. The subject, therefore, of this debate, seems to have been, how Jesus, who had been himself baptized by John, came to rebaptize John's disciples, (Acts 19:4,) that is, assume greater authority than John, and virtually declare that his baptism was inefficacious for the purposes of purification. And they came unto John The Baptist's disciples, though they had often heard their master speak on the subject, not understanding the subserviency of his ministry to that of Jesus, were unable to give their antagonists a satisfactory answer, so they came and proposed their question to John himself; and said, He to whom thou barest witness Gavest such an honourable testimony; behold, the same baptizeth People that come to him from all parts, yea, even such as have before received thy baptism. They seem to have been apprehensive that this would cause John's baptism to be neglected, and would tend to the injury of his character.