Ibn Abbas (Allah be pleased with them) reported:It was proposed that he (the Holy Prophet) be married to the daughter of Hamza, whereupon he said: She is not lawful for me for she is the daughter of my foster-brother, and that is unlawful by reason of fosterage what is unlawful by reason of genealogy

A hadith like this is narrated on the authority of Hammam, Sa'id, Bishr b 'Umar, but with a small variation of words