Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4567
It has been narrated (through a still different chain of transmitters) on the Same authority (i. e. 'Arfaja) who said similarly-but adding:" Kill all of them." I heard the Messenger of Allah (may peace be upon him) say: When you are holding to one single man as your leader, you should kill who seeks to undermine your solidarity or disrupt your unity.