Sahih Muslim Book 012, Hadith Number 3964.
Chapter : Disapproval of giving preference to tome children while making donation.
Nu'man b. Bashir reported that his father had donated a slave to him. Allah's Apostle (may peace he upon him) said: Who is this slave (how have you come to possess it)? Thereupon he (Nu'man b. Bashir) said: My father has donated it to me, whereupon he said: Have all brothers (of yours) been given this gift as given to you? He said: No. Thereupon he (the Holy Prophet) said: Then return him.