Sahih Bukhari Volume 003, Book 048, Hadith Number 812.
Narated By 'Aisha : Aflah asked the permission to visit me but I did not allow him. He said, "Do you veil yourself before me although I am your uncle?" 'Aisha said, "How is that?" Aflah replied, "You were suckled by my brother's wife with my brother's milk." I asked Allah's Apostle about it, and he said, "Allah is right, so permit him to visit you."