What did Ibn Umar disapprove of when the man asked him why he wasn't fighting, according to the hadith narrated about Prophet Muhammad (saw)?
 Narrated Ibn `Umar:                     That a man came to him (while two groups of Muslims were fighting) and said, "O Abu `Abdur Rahman! Don't you hear what Allah has mentioned in His Book: 'And if two groups of believers fight against each other...' (49.9) So what prevents you from fighting as Allah has mentioned in His Book?"' Ibn `Umar said, "O son of my brother! I would rather be blamed for not fighting because of this Verse than to be blamed because of another Verse where Allah says: 'And whoever kills a believer intentionally..." (4.93) Then that man said, "Allah says:-- 'And fight them until there is no more afflictions (worshipping other besides Allah) and the religion (i.e. worship) will be all for Allah (Alone)" (8.39) Ibn `Umar said, "We did this during the lifetime of Allah's Apostle when the number of Muslims was small, and a man was put to trial because of his religion, the pagans would either kill or chain him; but when the Muslims increased (and Islam spread), there was no persecution." When that man saw that Ibn `Umar did not agree to his proposal, he said, "What is your opinion regarding `Ali and `Uthman?" Ibn `Umar said, "What is my opinion regarding `Ali and `Uthman? As for `Uthman, Allah forgave him and you disliked to forgive him, and `Ali is the cousin and son-in-law of Allah's Apostle ." Then he pointed out with his hand and said, "And that is his daughter's (house) which you can see."