It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) was asked to marry the daughter of Hamzah, and he (peace and blessings be upon him) said: "She is not lawful for me; she is the daughter of my foster brother, and whatever relations are forbidden through lineage are forbidden through nursing."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2909