"She is the daughter of my brother through breast-feeding, and what becomes unlawful (for marriage) through breast-feeding is the same as that which becomes unlawful through lineage." (Using translation from Nasāʾī 3306)
أَنَّ رَسُولَ اللهِ ﷺ أُرِيدَ عَلَى ابْنَةِ حَمْزَةَ أَنْ يَتَزَوَّجَهَافَقَالَ إِنَّهَا ابْنَةُ أَخِي مِنَ الرَّضَاعَةِ فَإِنَّهُ يَحْرُمُ مِنَ الرَّضَاعِ مَا يَحْرُمُ مِنَ النَّسَبِ