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 the daughter of my foster brother, and Allah, the Mighty and Majestic, forbids through nursing whatever relations He forbids through lineage."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2910