Sahih Muslim Book 012, Hadith Number 3969.
Chapter : Disapproval of giving preference to tome children while making donation.
Nu'man b. Bashir (Allah be pleased with them) reported: My father took me to Allah's Messenger (may peace be upon him) and said: Allah's Messenger, bear witness that I have given such and such gift to Nu'man from my property, whereupon he (the Holy Prophet) said: Have you conferred upon all of your sons as you have conferred upon Nu'man? He said: No. Thereupon he (the Holy Prophet) said: Call someone else besides me as a witness. And he further said: Would it, please you that they (your children) should all behave virtuously towards you? He said: Yes. He (the Holy Prophet) said: Then don't do that (i e. don't give gift to one to the exclusion of others).