The Messenger of Allah ﷺ said, "Reconciliation between Muslims is permissible."
قال رسول الله ﷺ: الصلح جائز بين المسلمين.
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Abu Dawud narrated it (3594) through two routes. The first, from Sulayman bin Dawud Mahri, who said Ibn Wahb informed us, who said Sulayman bin Bilal informed me. The second, from Ahmad bin Abdul-Wahid Dimashqi, who said Marwan, meaning Ibn Muhammad, told us, who said Sulayman bin Bilal, or Abdul-Aziz bin Muhammad, the shaykh was uncertain, told us, who said Kathir bin Zayd told us, from Walid bin Rabah, from Abu Hurairah, who said, then he mentioned it.Abu Dawud said, Ahmad (Ibn Abdul-Wahhab) added, "except a reconciliation that permits something forbidden or forbids something permitted," and Sulayman bin Dawud added, "Muslims are bound by their conditions."Ibn Hibban (5091) and Hakim (2/49) both graded it sahih, both from the hadith of Sulayman bin Bilal with his chain, and mentioned it with his chain, and Hakim mentioned the narration of Sulayman bin Bilal just as Abu Dawud said. As for Ibn Hibban, he mentioned something like the statement of Ibn Abdul-Wahhab, but he did not mention the addition that Sulayman bin Bilal mentioned.Ibn Jarud narrated it (637-638) through another route from Kathir bin Zayd, and added in it, "whatever agrees with the truth."Hakim said, "The narrators of this hadith are from Madinah, and the two of them did not include it, and this is a foundational principle in the book." Dhahabi responded to him, saying, "He did not grade it sahih, and Kathir was graded daif by Nasai, while others considered him acceptable."I say, its chain is hasan because of the discussion regarding Kathir bin Zayd. Ahmad said, "I see no harm in him." Ibn Adi said, "I hope there is no harm in him." Ibn Hibban mentioned him among the reliable narrators, and included his narrations in his Sahih.The hadith has another chain, which is what Daraqutni (3/27) and Hakim (2/50) narrated, both from the hadith of Abdullah bin Husayn Masissi, who said Uthman told us, who said Hammad bin Zayd told us, from Thabit, from Abu Rafi, from Abu Hurairah, who said, the Messenger of Allah ﷺ said, "Reconciliation is permissible between Muslims."Hakim said, "Sahih according to the criterion of the two shaykhs, and it is known through Abdullah bin Husayn Masissi, who is reliable." This is how it appears in the printed Mustadrak, but what Ibn Hajar mentioned in Lisan Mizan (3/273), in the biography of Abdullah bin Husayn, of Hakim's statement is, "Sahih, Abdullah bin Husayn Masissi narrated it alone, and he is reliable." Dhahabi likewise mentioned it in his summary.Dhahabi responded to him, saying, "Ibn Hibban said, 'He steals hadith.'" I say, his statement in Majruhin (575) is, "He settled in Masissa, he distorts reports and steals them, it is not permissible to rely on him when he narrates alone."The hadith, taken together through these two routes, reaches the level of hasan.As for what Kathir bin Abdullah bin Amr bin Awf Muzani narrated, from his father, from his grandfather, that the Messenger of Allah ﷺ said, "Reconciliation is permissible between Muslims except a reconciliation that forbids something permitted or permits something forbidden, and Muslims are bound by their conditions except a condition that forbids something permitted or permits something forbidden," this is extremely daif.Tirmidhi (1352), Ibn Majah (2353), Daraqutni (3/27), Hakim (4/101), and Bayhaqi (6/65) all narrated it, all through the route of Kathir bin Abdullah bin Amr bin Awf with his chain. Tirmidhi said, "This is a hasan sahih hadith." But it is not as he said, rather its chain is extremely daif, for Kathir bin Abdullah is abandoned as a narrator and a liar.Ibn Hibban said, "He narrates from his father, from his grandfather, a fabricated collection, it is not permissible to mention it in books nor to narrate from him except by way of expressing astonishment." Therefore Tirmidhi was criticized for grading this hadith sahih. Dhahabi said in his biography in Mizan (3/407), "For this reason, scholars do not rely on Tirmidhi's grading of sahih."It has other supporting narrations from Ayesha, Anas bin Malik, Rafi bin Khadij, and Ibn Umar, but there is criticism in all of them. The abundance of these supporting narrations indicates that the hadith has a basis, and the best of them is the hadith of Abu Hurairah.Ibn Abu Shayba narrated in Musannaf, with his chain, from Ataa, who said, "It reached us that the Messenger of Allah ﷺ said, 'Believers are bound by their conditions.'" This is a sahih mursal narration which strengthens the basis of the hadith, and the jurists received it with acceptance, and derived from it many rulings.