Sahih Bukhari Volume 006, Book 060, Hadith Number 040.
Narrated By Nafi' : During the affliction of Ibn Az-Zubair, two men came to Ibn 'Umar and said, "The people are lost, and you are the son of 'Umar, and the companion of the Prophet, so what forbids you from coming out?" He said, "What forbids me is that Allah has prohibited the shedding of my brother's blood." They both said, "Didn't Allah say, 'And fight then until there is no more affliction?" He said "We fought until there was no more affliction and the worship is for Allah (Alone while you want to fight until there is affliction and until the worship become for other than Allah."
Narrated Nafi (through another group of sub-narrators): A man came to Ibn 'Umar and said, "O Abu Abdur Rahman! What made you perform Hajj in one year and Umra in another year and leave the Jihad for Allah' Cause though you know how much Allah recommends it?" Ibn 'Umar replied, "O son of my brother! Islam is founded on five principles, i.e. believe in Allah and His Apostle, the five compulsory prayers, the fasting of the month of Ramadan, the payment of Zakat, and the Hajj to the House (of Allah)." The man said, "O Abu Abdur Rahman! Won't you listen to why Allah has mentioned in His Book: 'If two groups of believers fight each other, then make peace between them, but if one of them transgresses beyond bounds against the other, then you all fight against the one that transgresses. (49.9) and: "And fight them till there is no more affliction (i.e. no more worshiping of others along with Allah)." Ibn 'Umar said, "We did it, during the lifetime of Allah's Apostle when Islam had only a few followers. A man would be put to trial because of his religion; he would either be killed or tortured. But when the Muslims increased, there was no more afflictions or oppressions." The man said, "What is your opinion about 'Uthman and 'Ali?" Ibn 'Umar said, "As for 'Uthman, it seems that Allah has forgiven him, but you people dislike that he should be forgiven. And as for 'Ali, he is the cousin of Allah's Apostle and his son-in-law." Then he pointed with his hand and said, "That is his house which you see."