Bukhari

Hadith Commentary:
What happened was that Abu Musa Ash'ari radi Allahu anhu was the governor of Kufa on behalf of Uthman radi Allahu anhu.
Ali radi Allahu anhu kept him in his position.
When Aisha radi Allahu anha, accompanied by a large army, went to Basra, and both Talha and Zubair radi Allahu anhuma broke their pledge of allegiance to Ali radi Allahu anhu and joined her, Ali radi Allahu anhu sent word to Abu Musa radi Allahu anhu to keep the Muslims prepared for battle and to support the truth.
Abu Musa radi Allahu anhu consulted Sa’ib bin Malik Ash’ari for advice.
He also advised that the command of the current Caliph should be followed, but Abu Musa radi Allahu anhu did not listen and began telling people not to intend for war.
Eventually, Ali radi Allahu anhu appointed Qarzah bin Ka’b as the governor of Kufa and dismissed Abu Musa radi Allahu anhu.
Meanwhile, Talha and Zubair radi Allahu anhuma, upon reaching Basra, arrested Ibn Hunayf, the deputy of Ali radi Allahu anhu.
This was open rebellion and breach of covenant, and fighting such people was necessary according to the explicit text of the Qur’an (فَقَاتِلُوا الَّتِي تَبْغِي حَتَّى تَفِيءَ إِلَى أَمْرِ اللَّهِ) (al-Hujurat: 9) .
And the opinion of Ammar radi Allahu anhu was absolutely correct that there should be no delay in obeying the command of the current Caliph.
And the Messenger of Allah sallallahu alayhi wa sallam himself had said to Ali radi Allahu anhu: “O Ali! You will fight those who break their pledge and the rebels.”
It is said that when the Battle of Jamal began, on the 15th of Jumada al-Ula, 36 AH, a person came to Ali radi Allahu anhu and said, “How do you fight these people?” He replied, “I fight upon the truth.”
He said, “They also say, ‘We fight upon the truth.’”
Ali radi Allahu anhu replied, “I fight them because of their breaking the pledge and abandoning the community.”
May Allah forgive them all.

Hadith Commentary:
1.
In Kufa, Abu Musa al-Ash‘ari radi Allahu anhu was the governor on behalf of Uthman radi Allahu anhu, while Abu Mas‘ud al-Ansari radi Allahu anhu supported Ali radi Allahu anhu. However, during the times of tribulation, the position of both these noble companions was that they should not participate in it at all, as is evident from multiple ahadith.
In contrast, the opinion of Ammar radi Allahu anhu was that in such circumstances, it is necessary to support the rightly guided caliph (khalifah rashid).
And it is obligatory to restrain the rebellious people by force and opposition.
2.
The commentator of Sahih al-Bukhari, Ibn Battal, has said that the aforementioned gathering took place in the house of Abu Mas‘ud al-Ansari radi Allahu anhu, and he was a person of means and wealth.
Therefore, he gave a garment to both Ammar ibn Yasir radi Allahu anhu and Abu Musa al-Ash‘ari radi Allahu anhu.
Ammar radi Allahu anhu had just returned from a journey and was in a state of having fought.
Abu Mas‘ud radi Allahu anhu did not consider it appropriate for him to go to the mosque in that condition, and he also did not deem it suitable to present the garment only to Ammar radi Allahu anhu in the presence of Abu Musa al-Ash‘ari radi Allahu anhu. On this basis, he gave a garment to Abu Musa al-Ash‘ari radi Allahu anhu as well. Then all three of them proceeded to the central mosque of Kufa to perform the Friday prayer.
(Fath al-Bari: 13/75)