Sunan an-Nasa'i, Volume 4, Book 26, Hadith 3314 (DarusSalam) ⓘ

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."

أَخْبَرَنَا هَنَّادُ بْنُ السَّرِيِّ، فِي حَدِيثِهِ عَنْ أَبِي الأَحْوَصِ، عَنْ أَشْعَثَ بْنِ أَبِي الشَّعْثَاءِ، عَنْ أَبِيهِ، عَنْ مَسْرُوقٍ، قَالَ قَالَتْ عَائِشَةُ دَخَلَ عَلَىَّ رَسُولُ اللَّهِ صلى الله عليه وسلم وَعِنْدِي رَجُلٌ قَاعِدٌ فَاشْتَدَّ ذَلِكَ عَلَيْهِ وَرَأَيْتُ الْغَضَبَ فِي وَجْهِهِ فَقُلْتُ يَا رَسُولَ اللَّهِ إِنَّهُ أَخِي مِنَ الرَّضَاعَةِ ‏.‏ فَقَالَ ‏ "‏ انْظُرْنَ مَا إِخْوَانُكُنَّ - وَمَرَّةً أُخْرَى - انْظُرْنَ مَنْ إِخْوَانُكُنَّ مِنَ الرَّضَاعَةِ فَإِنَّ الرَّضَاعَةَ مِنَ الْمَجَاعَةِ ‏" ‏ ‏.‏