He said that when the people of Madinah renounced their allegiance to Yazid bin Muawiya, Ibn Umar gathered his household and his children and said, "I heard the Prophet ﷺ say, 'A banner will be raised for every traitor on the Day of Resurrection.' We have pledged allegiance to this man on the terms set by Allah and His Messenger, and I know of no treachery greater than for a man to pledge allegiance on the terms set by Allah and His Messenger, and then take up arms against him. I warn you, if I learn that any one of you has renounced his allegiance to him or pledged allegiance to anyone else in this matter, that will be the parting between me and him."
قال لما خلع أهل المدينة يزيد بن معاوية جمع ابن عمر حشمه وولده فقال إني سمعت النبي ﷺ يقول: ينصب لكل غادر لواء يوم القيامة… وإنا قد بايعنا هذا الرجل على بيع الله ورسوله، وإني لا أعلم غدرا أعظم من أن يبايع رجل على بيع الله ورسوله، ثم ينصب له القتال، وإني لا أعلم أحدا منكم خلعه، ولا بايع في هذا الأمر، إلا كانت الفيصل بيني وبينه.
Bukhari narrated it in the Book of Tribulations (7111), from Sulayman bin Harb, from Hammad bin Zayd, from Nafi, who mentioned it. Muslim narrated it in the Book of Jihad and Expeditions (1735:9), from Abu Rabi Utaki, from Hammad, from Ayub, from Nafi, from Ibn Umar, restricting it to the raised portion of the hadith without the accompanying story.His saying, "the separation," means the severance and estrangement.Ibn Hajar said, "This hadith establishes the obligation of obeying the leader to whom the pledge of allegiance has been validly given, and the prohibition of rebelling against him, even if he acts unjustly in his rulings, and that he is not stripped of his authority through wrongdoing." Fath al-Bari (13/71).