Musnad Ahmad 26:94

I heard Yahya, who said: I heard Sulayman, who said: I heard Zayd ibn Wahb, who said: I heard Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to us: "You will see after me favoritism and matters that you will disapprove of." He said: We said: "What do you command us?" He said: "Render to them their right, and ask Allah for your right."