al-Fadl bin Musa al-Synany الفضل بن موسى السيناني · The Book of al-Bay'ah

'No prophet has eve been sent, nor has there been any Khalifah after him, but he has two groups of advisers, a group that tells him to do good and a group that tells him to do evil. Whoever is protected from the evil group, then he is indeed protected.