Link 3 from the end of the chain
Narrated Abu Wail: We were in Siffin and Sahl bin Hunaif got up and said, "O people! Blame yourselves! We were with the Prophet (ﷺ) on the day of Hudaibiya, and if we had been called to fight, we would have fought. But `Umar bin Al Khatab came and said, 'O Allah's Messenger (ﷺ)! Aren't we in the right and our opponents in the wrongs' Allah's Messenger (ﷺ) said, 'Yes.' `Umar said, 'Aren't our killed persons in Paradise and their's in Hell?' He said, 'Yes.' `Umar said, 'Then why should we accept hard terms in matters concerning our religion? Shall we return before Allah judges between us and them?' Allah's Messenger (ﷺ) said, 'O Ibn Al- Khattab! I am the Messenger of Allah and Allah will never degrade me. Then `Umar went to Abu Bakr and told him the same as he had told the Prophet. On that Abu Bakr said (to `Umar). 'He is the Messenger of Allah and Allah will never degrade him.' Then Surat-al-Fath (i.e. Victory) was revealed and Allah's Messenger (ﷺ) recited it to the end in front of `Umar. On that `Umar asked, 'O Allah's Messenger (ﷺ)! Was it (i.e. the Hudaibiya Treaty) a victory?' Allah's Messenger (ﷺ) said, "Yes".
Link 2 from the end of the chain
Narrated Habib bin Abi Thabit: I went to Abu Wail to ask him (about those who had rebelled against `Ali). On that Abu Wail said, "We were at Siffin (a city on the bank of the Euphrates, the place where me battle took place between `Ali and Muawiya) A man said, "Will you be on the side of those who are called to consult Allah's Book (to settle the dispute)?" `Ali said, 'Yes (I agree that we should settle the matter in the light of the Qur'an)." ' Some people objected to `Ali's agreement and wanted to fight. On that Sahl bin Hunaif said, 'Blame yourselves! I remember how, on the day of Al-Hudaibiya (i.e. the peace treaty between the Prophet (ﷺ) and the Quraish pagans), if we had been allowed to choose fighting, we would have fought (the pagans). At that time `Umar came (to the Prophet) and said, "Aren't we on the right (path) and they (pagans) in the wrong? Won't our killed persons go to Paradise, and theirs in the Fire?" The Prophet replied, "Yes." `Umar further said, "Then why should we let our religion be degraded and return before Allah has settled the matter between us?" The Prophet (ﷺ) said, "O the son of Al-Khattab! No doubt, I am Allah's Messenger (ﷺ) and Allah will never neglect me." So `Umar left the place angrily and he was so impatient that he went to Abu Bakr and said, "O Abu Bakr! Aren't we on the right (path) and they (pagans) on the wrong?" Abu Bakr said, "O the son of Al-Khattab! He is Allah's Messenger (ﷺ), and Allah will never neglect him." Then Sura Al-Fath (The Victory) was revealed."
