The Prophet ﷺ used to say, "The Muslim is the brother of the Muslim. He does not wrong him nor abandon him."He also used to say, "By the One in whose hand is the soul of Muhammad, no two people love one another and then become separated except because of a sin that one of them commits."And he used to say, "A Muslim owes his fellow Muslim six acts of kindness. He should bless him when he sneezes, visit him when he is sick, give him sincere counsel whether he is present or absent, greet him with peace when he meets him, respond when he invites him, and follow his funeral when he dies."And he forbade a Muslim from shunning his brother for more than three days.
حدثنا موسى بن داود حدثنا ابن لهيعة عن خالد بن أبي عمران عن نافع
أن النبي ﷺ كان يقول المسلم أخو المسلم لا يظلمه ولا يخذله ويقول والذي نفس محمد بيده ما تواد اثنان ففرق بينهما إلا بذنب يحدثه أحدهما وكان يقول للمرء المسلم على أخيه من المعروف ست يشمته إذا عطس ويعوده إذا مرض وينصحه إذا غاب ويشهده ويسلم عليه إذا لقيه ويجيبه إذا دعاه ويتبعه إذا مات ونهى عن هجرة المسلم أخاه فوق ثلاث
Its isnad is sahih, and it is in Majma al-Zawaid 8:184, except for its ending, "the prohibition of a Muslim shunning his brother for more than three days," and he said, Ahmad narrated it, and its isnad is hasan. I do not know why Haythami omitted the end of the hadith, since it is not in the Six Books from the hadith of Ibn Umar, as far as I know. He mentioned it in the Zawaid 8:67 from Ibn Umar as a marfu report, "It is not permissible for a believer to shun his brother for more than three days," and said, Tabarani narrated it in Al-Awsat with two isnads, one of them daif, and in the other is Ibrahim bin Abu Usayd, whom I do not know! It would have been more fitting for him to mention the one here, which has a sahih isnad, or at least hasan by his own standard. What is even more strange is that he mentions the beginning of the hadith, "A Muslim is the brother of a Muslim, he does not wrong him nor abandon him," even though this is established in the Sahihayn and elsewhere from the hadith of Ibn Umar, in a different context, so he left out what belongs among the Zawaid in favor of what does not belong among them! See Targheeb wal-Tarheeb 3:250, and Sahih Muslim 2:283, and see what has already passed in the Musnad of Ali, 673, 674, and in the Musnad of Saad, 1589.