Amir al-Mu'minin
Caliph Omar has been reported to have said: "O Muslims, straighten me with your hands when I go wrong", and at that instance, a Muslim man stood up and said, "O Amir al-Mu'minin (Leader of the Believers) if you are not straightened by our hands we will use our sword to straighten you!". Hearing this Caliph Omar said "Alhamdulillah (Praise be to Allah) I have such followers."