"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."
Sunan an-Nasa'i Book 26, Hadith 117
← Previous Hadith "We wrote to Ibrahim bin Yazid An-Nakha'i asking him about breast-feeding. He wrote back saying that Shuraih had narrated that 'Ali and Ibn Mas'ud used to say: 'A little or a lot of breast-feeding makes marriage prohibited.'" In his book, it said that Abu Ash-Sha'tha' Al-Muharibi narrated that 'Aishah had told him that the Prophet of Allah used to say: "Suckling (Al-Khatfah) once or twice does not make (marriage) prohibited."

Sunan an-Nasa'i Book 26, Hadith 116 Next Hadith → "I said: 'O Messenger of Allah, there is a man asking permission to enter your house.' The Messenger of Allah said: 'I think it is so-and-so the paternal uncle of Hafsah through breast-feeding.' 'Aishah said: If so-and-so (her own paternal uncle through breast-feeding) were alive, would he be allowed to enter upon me?' The Messenger of Allah said: 'What becomes unlawful (for marriage) through breast-feeding is that which becomes unlawful through birth.'"

Sunan an-Nasa'i Book 26, Hadith 118