Sunan an-Nasa'i 3301

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