كتاب الرضاع
17  
The Book of Suckling
(3)
Chapter: The daughter of one's brother through breastfeeding is forbidden in marriage
(3)
باب تَحْرِيمِ ابْنَةِ الأَخِ مِنَ الرَّضَاعَةِ ‏
Sahih Muslim 1446 a

'Ali (Allah be pleased with him) reported having said this:

Messenger of Allah, why is it that you select (your wife) from among the Quraish, but you ignore us (the nearest of the kin)? Thereupon he said: Have you anything for me (a suitable match for me)? I said; Yes, the daughter of Hamza, whereupon Allah's Messenger (ﷺ) said: She is not lawful for me, for she is the daughter of my brother by reason of fosterage.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَزُهَيْرُ بْنُ حَرْبٍ، وَمُحَمَّدُ بْنُ الْعَلاَءِ، - وَاللَّفْظُ لأَبِي بَكْرٍ - قَالُوا حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ سَعْدِ بْنِ عُبَيْدَةَ، عَنْ أَبِي عَبْدِ الرَّحْمَنِ، عَنْ عَلِيٍّ، قَالَ قُلْتُ يَا رَسُولَ اللَّهِ مَا لَكَ تَنَوَّقُ فِي قُرَيْشٍ وَتَدَعُنَا فَقَالَ ‏"‏ وَعِنْدَكُمْ شَىْءٌ ‏"‏ ‏.‏ قُلْتُ نَعَمْ بِنْتُ حَمْزَةَ ‏.‏ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّهَا لاَ تَحِلُّ لِي إِنَّهَا ابْنَةُ أَخِي مِنَ الرَّضَاعَةِ ‏"‏ ‏.‏
Reference : Sahih Muslim 1446a
In-book reference : Book 17, Hadith 14
USC-MSA web (English) reference : Book 8, Hadith 3407
  (deprecated numbering scheme)