Oath of allegiance (bay‘ah) of ‘Ali ibn Abi Taalib to Abu Bakr as-Siddeeq (may Allah be pleased with them both)

The swearing of allegiance (bay‘ah) by ‘Ali ibn Abi Taalib (may Allah be pleased with him) [to Abu Bakr] is proven in as-Saheehayn (al-Bukhaari and Muslim), even though it happened a few months late.
It was narrated from ‘Aa’ishah (may Allah be pleased with her) that her father Abu Bakr (may Allah be pleased with him) entered upon ‘Ali ibn Abi Taalib (may Allah be pleased with him) after he requested a meeting with him:
‘Ali ibn Abi Taalib recited the Tashahhud, then he said: O Abu Bakr, we acknowledge your virtue and what Allah has given you. We do not envy you for any favour that Allah has bestowed upon you, but you did it without consulting us and we thought that we had the right (to be consulted) because of our kinship with the Messenger of Allah (blessings and peace of Allah be upon him). He kept speaking to Abu Bakr until Abu Bakr’s eyes filled with tears. When Abu Bakr spoke, he said: By the One in Whose hand is my soul, kinship with the Messenger of Allah (blessings and peace of Allah be upon him) is dearer to me than kinship with my own people. As for this dispute that occurred between me and you concerning these properties, I have not deviated from the right path with regard to them, and I have not given up something that I saw the Messenger of Allah (blessings and peace of Allah be upon him) do with them, rather I have done it too.
‘Ali said to Abu Bakr: Your appointment for my oath of allegiance is this afternoon. When Abu Bakr had prayed Zuhr, he ascended the minbar and recited the tashahhud, and he spoke of ‘Ali and his delay in swearing allegiance, and the excuse that he had given, then he prayed for his forgiveness. And ‘Ali ibn Abi Taalib recited the tashahhud and spoke highly of Abu Bakr, and said that what he had done was not due to jealousy of Abu Bakr, or a refusal to accept the favour that Allah had bestowed upon him, but we thought that we should have had a share in the matter, but it had been decided without consulting us, and we were upset with that. The Muslims were pleased with this and said: You have done the right thing. Then the Muslims became closer to ‘Ali, when he did the right thing.
Narrated by al-Bukhaari (3998) and Muslim (1759).
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said:
It was as if they excused him for not coming to swear allegiance to Abu Bakr whilst Faatimah was still alive, because he was preoccupied with caring for her during her illness, and consoling her for the grief she felt at the loss of her father (blessings and peace of Allah be upon him). Moreover, when she got upset with Abu Bakr’s response when she asked him about inheritance, ‘Ali decided to go along with her in keeping away from him.
End quite. Fath al-Baari (7/494)
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
It is known from mutawaatir reports that no one refrained from swearing allegiance to him – namely Abu Bakr as-Siddeeq (may Allah be pleased with him) – except Sa‘d ibn ‘Ubaadah. As for ‘Ali and Banu Haashim, all of them swore allegiance to him, according to scholarly consensus, and none of them died without having sworn allegiance to him. However it was said that ‘Ali delayed his oath of allegiance for six months; it was also said that in fact he swore allegiance to him on the second day. Whatever the case, they swore allegiance to him without being forced to do so. End quote.
Minhaaj as-Sunnah (8/232)