John Chrysostom (attributed)

But if it be true that he who offers a cup of water does not lose his reward, consequently he who has been wronged but by a single word of calumny, shall not be without a reward. But that the reviled may have a claim to this blessing, two things are necessary, it must be false, and it must be for God’s sake; otherwise he has not the reward of this blessing; therefore He adds, falsely for my sake.