The Messenger of Allah ﷺ established a pact of brotherhood between the Emigrants and the Helpers in the house of Anas bin Malik.
حدثنا عفان حدثنا حماد بن سلمة حدثنا عاصم الأحول
حالف رسول الله ﷺ بين المهاجرين والأنصار في دار أنس بن مالك
Its isnad is sahih. See Sahih Bukhari 3/126, in the chapter on suretyship, regarding the words of Allah Almighty, "And those with whom your right hands have made a pledge" [Nisa 4:33], and Sahih Muslim 4/1960, no. 2529, in the chapter on the virtues of the companions, on the Prophet's ﷺ fostering brotherhood between the emigrants and the helpers, and Sunan Abu Dawud 3/338, no. 2925, in the chapter on inheritance shares, on the oath of alliance.