Narrated Aisha, Ummul Mu’minin: The Messenger of Allah (peace be upon him) said: When Allah has a good purpose for a ruler, He appoints for him a sincere minister who reminds him if he forgets and helps him if he remembers; but when Allah has a different purpose from that for him. He appoints for him an evil minister who does not remind him if he forgets and does not help him if he remembers.
Sunan Abi Dawud, Book 20, Hadith 5