Musannaf Ibn Abi Shayba 17:964

Ghundar narrated to us, from Shu'bah, from 'Asim, who said: I said to Qasim, "Is it disliked for a man to praise his brother while he is present?" He said, "Yes." I said, "What if he mentions him with the best of mentions while he is absent?" He said, "It used to be said: Do not praise your brother."