Musnad Abu Ya'la al-Mawsili 42:327

Zuhayr narrated to us, Abd al-Samad narrated to us, my father narrated to us, Muhammad ibn Jahadah narrated to us, from al-Walid, from Abdullah al-Bahiy, from Abu Sa’id, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There will be over you leaders to whom hearts will be tranquil and skins will be soft. Then there will be over you leaders from whom skins will shudder and hearts will be repulsed." A man said: "O Messenger of Allah, shall we not fight them?" He said: "No, as long as they establish the prayer."