مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3213
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: It was said to the Prophet (ﷺ): Why don't you marry the daughter of Hamzah? He said: "She is the daughter of my brother through breastfeeding.”
Musnad Ahmad 3237Its isnad is saheeh, al-Bukhari (2645) and Muslim (1447)]