Nafi' (may Allah have mercy on him) says that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) gathered the people of his household. When the people of Madinah had joined Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with him) and had abandoned Yazid bin Mu'awiyah, he (may Allah be pleased with him) said: We pledged allegiance to this man upon (the pledge of) Allah and His Messenger, and I heard the Prophet (peace and blessings be upon him) say: "For every betrayer there will be a banner on the Day of Resurrection, and it will be said: 'This is the betrayal of so-and-so.' And after associating partners with Allah, the greatest betrayal is that a man pledges allegiance to someone in the name of Allah and His Messenger and then breaks his pledge." So let none of you break the pledge to Yazid, and let no one step forward in this matter; whoever does so, there is a severance between me and him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16631