Sunan An-Nasa'i

It was narrated that Masruq said:""Aishah said: 'The Messenger of Allah entered upon me and there was a man sitting with me. He got upset about that, and I saw the anger in his face.' I said: ""O Messenger of Allah, he is my brother through breast-feeding."" He said: ""Be careful who you count as your brothers"" --or: ""be careful who you count as your brothers through breast-feeding""-- ""for the breast-feeding (which makes marriage prohibited) is from hunger