Believer is like a camel having a (pricking) bridle

Abdur-Rahman ibn Amr as-Salami said that he heard Irbaad ibn Sarriyah (Radhi Allahu Anhu) saying, “Allah’s Messenger (Sallallahu Alayhi wa Sallam) delivered a sermon to us whereby the eyes welled forth tears and the hearts were softened. We said, “Allah’s Messenger, this is a sermon of a person bidding farewell! So what do you enjoin upon us?” he said:

“I am leaving you on brightness, its night is (as bright) as its day. None would deviate from it except the one who is doomed to perish. Whosoever survives would see many differences. Then it would be incumbent upon you to adhere to my Sunnah and the Sunnah of the righteous and pious caliphs, with which you are familiar. Hold fast to it with your teeth and obedience (to the ruler) is obligatory upon you even if he is an Abyssinian slave. Verily the (true) Believer is like a camel having a (pricking) bridle in its nose. To whichever direction it is driven, it surrenders in submission.

(Sunan ibn Majah 1/13-4/41)