Musnad Ahmad 30:2810

'Abd al-Rahman narrated to us, Shu'bah narrated to us, he said: Mansur wrote to me that he heard Abu 'Uthman narrating from Abu Hurayrah, who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him)—the truthful, the believed, the possessor of this chamber—saying: "Mercy is not snatched away except from a wretched person."