It was narrated from 'Aishah that her paternal uncle through breast-feeding, whose name was Aflah, asked permission to meet her, and she observed Hijab before him. The Messenger of Allah was told about that and he said:"Do not observe Hijab before him, for what becomes unlawful (for marriage) through breast-feeding is that which becomes unlawful through lineage."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ يَزِيدَ بْنِ أَبِي حَبِيبٍ، عَنْ عِرَاكٍ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، أَنَّهَا أَخْبَرَتْهُ أَنَّ عَمَّهَا مِنَ الرَّضَاعَةِ يُسَمَّى أَفْلَحَ اسْتَأْذَنَ عَلَيْهَا فَحَجَبَتْهُ فَأُخْبِرَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَقَالَ " لاَ تَحْتَجِبِي مِنْهُ فَإِنَّهُ يَحْرُمُ مِنَ الرَّضَاعِ مَا يَحْرُمُ مِنَ النَّسَبِ " .
Nesai
The Book of Marriage • Hadith 3301