Augustine of Hippo
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.
(de Con. Evan. 4. 6) By which He shews, that he of whom John had spoken was not so far separated from the fellowship of the disciples, as to reject it, as a heretic, but as men are wont to hang back from receiving the Sacraments of Christ, and yet favour the Christian name, so as even to succour Christians, and do them service only because they are Christians. Of these He says they shall not lose their reward; not that they ought already to think themselves secure on account of this good will which they have towards Christians, without being washed with His baptism, and incorporated in His unity, but that they are already so guided by the mercy of God, as also to attain to these, and thus to go away from this life in security.