John Gill Commentary John 3:25

"There arose therefore a questioning on the part of John`s disciples with a Jew about purifying." — John 3:25 (ASV)

Then a question arose, a dispute or controversy caused by the baptism of John and Christ: between [some] of John's disciples and the Jews. The Syriac and Persic versions read, "between one of John's disciples, and a certain Jew"; and Nonnus renders it, "with an Hebrew man"; and so the Alexandrian manuscript; many others read, "with a Jew".

The contention between them was about purifying: either about the ceremonial purifications and ablutions commanded in the law of Moses, or concerning the various washings of persons and vessels according to the traditions of the elders, which the Jews in common were very tenacious of, and which they thought were brought into neglect and contempt by the baptism of John.

This seems to have been caused by the baptism of Christ, which the Jew might use against the disciple of John and urge that since another, besides his master, had set up baptizing, who could tell which was most right and safest to follow? Therefore, it would have been much better if no such rite at all had been used by any, but that the purifications required by the law of Moses and by their elders had been strictly and solely attended to.