From Sahih Muslim (Hadith 3571):
A'isha (Allah be pleased with her) reported that Aflah, the brother of Abu'l-Qu'ais, who was her uncle by reason of fosterage, came, and asked her permission (to enter the house) after seclusion (Hijab) was instituted. I refused to admit him. When Allah's Messenger (ﷺ) came, I informed him what I had done. He commanded me to grant him permission (as the brother of her foster-father was also her uncle)
Reference: Muslim 3571