Sayyiduna Ibn Umar (may Allah be pleased with them both) narrated that a man came to him and said: O Abu Abd al-Rahman, do you not hear what Allah has mentioned in His Book: "And if two groups of the believers fight one another" [Surah al-Hujurat: 9]? So what prevents you from fighting as Allah has mentioned in His Book? He said: O my nephew, to be reproached with this verse while not fighting is dearer to me than to be reproached with the verse that Allah, the Mighty and Majestic, said before it: "And whoever kills a believer intentionally, his recompense is Hell" [Surah al-Nisa: 93]. The man said: But Allah has said: "And fight them until there is no fitnah" [Surah al-Baqarah: 193]. Ibn Umar said: We did that in the time of the Messenger of Allah (peace and blessings be upon him), when Islam was small and a man would be persecuted for his religion: they would either kill him or bind him, until Islam prevailed and there was no fitnah. When the man saw that he would not agree with him in what he wanted, he said: Then what do you say about Ali and Uthman (may Allah be pleased with them both)? Ibn Umar said: As for Uthman, Allah has pardoned him, but you disliked to pardon him. As for Ali, he is the cousin of the Messenger of Allah (peace and blessings be upon him) and his son-in-law; and he pointed with his hand and said: This is his house, where you see it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16806