Musannaf Ibn Abi Shayba 37:627

Waki’ narrated to us, from ‘Imran bin Hudayr, from al-Simt (al-Sumayt), from Ka’b, who said: For every era there are kings. If Allah intends good for a people, He sends among them their reformers. And if He intends evil for a people, He sends among them their affluent ones (those who live in luxury).