Sunan Abi Dawud, Hadith 2920

Narrated Anas bin Malik: The Messenger of Allah established an alliance (of brotherhood) between the Emigrants and the Helpers in our house. He was asked: Did not the Messenger of Allah say: There is no alliance in Islam ? He replied: The Messenger of Allah established an alliance between the Emigrants and the Helpers in our house. This he said twice or thrice.

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا سُفْيَانُ، عَنْ عَاصِمٍ الأَحْوَلِ، قَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ، يَقُولُ حَالَفَ رَسُولُ اللَّهِ صلى الله عليه وسلم بَيْنَ الْمُهَاجِرِينَ وَالأَنْصَارِ فِي دَارِنَا ‏.‏ فَقِيلَ لَهُ أَلَيْسَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ لاَ حِلْفَ فِي الإِسْلاَمِ ‏" ‏ ‏.‏ فَقَالَ حَالَفَ رَسُولُ اللَّهِ صلى الله عليه وسلم بَيْنَ الْمُهَاجِرِينَ وَالأَنْصَارِ فِي دَارِنَا ‏.‏ مَرَّتَيْنِ أَوْ ثَلاَثًا

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also referenced under: Hadith 2926 (DarusSalam)