Charles Ellicott Commentary Mark 10:38

"But Jesus said unto them, Ye know not what ye ask. Are ye able to drink the cup that I drink? or to be baptized with the baptism that I am baptized with?" — Mark 10:38 (ASV)

And be baptized with the baptism.—The clause seems to have been found originally in Mark only, and to have been added afterwards by the transcribers of Matthew to bring the reports of the two Gospels into more entire agreement.