Sahih Muslim Book 8, Hadith Number 3406.

Chapter: Kitab Al-Rada’a-Book pertaining to fosterage.

‘Aisha (Allah be pleased with her) reported: Aflah b. Qu’ais sought permission from me (to enter the house), but I refused to grant him the permission, and he sent me (the message saying): I am your uncle (in the sense) that the wife of my brother has suckled you, (but still) I refused to grant him permission. There came the Messenger of Allah (May peace be upon him) and I made a mention of it to him, and he said: He can enter (your house), for he is your uncle.