Musnad Ahmad 31:241

'Abd al-Samad narrated to us, my father narrated to us, and 'Affan said: 'Abd al-Warith narrated to us, Muhammad ibn Jahadah narrated to us, al-Walid narrated to me, from 'Abdullah al-Bahiy, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There will be leaders whose skins will be soft for them and hearts will be tranquil toward them, and there will be leaders over you from whom hearts will recoil and skins will shudder." They said: "Shall we not kill them?" He said: "No, as long as they establish the prayer."