Abdullah bin Mubarak عبد الله بن المبارك · The Book of al-Bay'ah

"O you who believe! Obey Allah and obey the Messenger (Muhammad). That he said: This was revealed concerning 'Abdullah bin Hudhaifah bin Qais bin 'Adiyy, whom the Messenger of Allah appointed in charge of an expedition"

'No ruler is appointed but he has tow groups of advisers: A group which urges him to do good and tells him not to do evil, and a group which does its best to corrupt him. Whoever is protected from their evil is indeed protected. And he (the ruler) belongs to the group that has the greater influence over him."