Pseudo-Chrysostom
Catena Aurea · Markusevangelium 9
And John answered him, saying, Master, we saw one casting out devils in thy name, and he followeth not us: and we forbad him, because he followeth not us. But Jesus said, Forbid him not: for there is no man which shall do a miracle in my name, that can lightly speak evil of me. For he that is not against us is on our part. For whosoever shall give you a cup of water to drink in my name, because ye belong to Christ, verily I say unto you, he shall not lose his reward. And whosoever shall offend one of these little ones that believe in me, it is better for him that a millstone were hanged about his neck, and he were cast into the sea.
(Vict. Ant. e Cat. in Marc.) It was not from jealousy or envy, however, that John wished to forbid him who cast out devils, but because he wished that all, who called on the name of the Lord, should follow Christ, and be one body with His disciples. But the Lord, however unworthy they who perform the miracles may be, incites others by their means to believe on Him, and induces themselves by this unspeakable grace to become better. Wherefore there follows: But Jesus said, Forbid him not.