Marco 9:29

And he said unto them, This kind can come forth by nothing, but by prayer and fasting. Prayer and fasting - See on Matteo 17:21 (note).

This demon may be considered as an emblem of deeply rooted vices, and inveterate habits, over which the conquest is not generally obtained, but through extraordinary humiliations.

This case is related by both Matthew and Luke, but it is greatly amplified in Mark's account, and many new circumstances related. Another proof that Mark did not abridge Matthew.