Nafi' said: A man came to Sayyiduna Ibn Umar (may Allah be pleased with them both) and said: Why do you hold back from this matter, when you are a Companion of the Messenger of Allah (peace and blessings be upon him) and the son of the Commander of the Believers? He said: "What holds me back from it is only that Allah, the Mighty and Majestic, has made the blood of my Muslim brother sacred for me." He said: But Allah, the Mighty and Majestic, says: "And fight them until there is no more fitnah and the religion is entirely for Allah" [Surah al-Anfal: 39]. At this Ibn Umar (may Allah be pleased with them both) said: "We fought them until there was no more fitnah and the religion was entirely for Allah, whereas you want me to fight so that fitnah arises anew and the religion becomes for other than Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12990