Introduction to System of Islam by Jalal Ansari

The department of Internal Security oversees everything connected with security inside the Islamic State, utilising the military forces for this purpose.

The internal security, as well as the external security, is preserved by the army. The functions of the (police) are under the control of the army. The Prophet (saw) appointed Qays ibn Sa‘ad as the head of security. He was there to protect the Prophet (saw) when he was in Majlis. It is preferable for the internal security force to maintain the procedures of the regular army, so that it will remain organised, efficient, and co-ordinated as in a regular army. The internal security force has the function of surveillance, preserving law and order, and to execute the laws adopted by the State. The Prophet (saw) appointed ‘Abdullah ibn Mas‘ud as the leader of assas (surveillance). Surveillance, by this part of the army, does not mean to invade the privacy of others. Rather, its usage is for general surveillance. Since maintaining the internal security is an action the State is responsible for, it has no right to levy payments on the citizens of the State for executing this function.