Abu Dawud Book 13, Hadith Number 2926.

Narated By ‘Aisha, Ummul Mu’minin : The Apostle of Allah (PBUH) 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.