From Sahih Muslim (Hadith 3606):
A'isha (Allah be pleased with her) reported:Allah's Messenger (ﷺ) visited me when a man was sitting near me, and he seemed to disapprove of that. And I saw signs of anger on his face and I said: Messenger of Allah, he is my brother by forsterage, whereupon he said: Consider who your brothers are because of fosterage since fosterage is through hunger (i. e. in infancy)
Reference: Muslim 3606