Sahih Muslim Book 20, Hadith Number 4545.

Chapter : Fulfilment of the covenant made with the Caliphs is imperative, the caliph to whom allegiance is sworn in the first instance has an established supremacy over those who assume powers.

It has been narrated on the authority of ‘Abdullah who said: The Messenger of Allah (may peace be upon him) said: After me there will be favouritism and many things that you will not like. They (his Companions) said: Messenger of Allah, what do you order that one should do it anyone from us has to live through such a time? He said: You should discharge your own responsibility (by obeying your Amir), and ask God to concede your right (by guiding the Amir to the right path or by replacing him by one more just and God-fearing).