Musnad Ahmad 937:40

Muhammad ibn Fudayl narrated to us, Fulayt al-Amiri narrated to me, from Jasrah al-Amiriyyah, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) prayed one night and recited one verse until morning, bowing with it and prostrating with it: "If You punish them, then indeed they are Your servants; and if You forgive them, then indeed it is You who is the Exalted in Might, the Wise" [Al-Ma'idah: 118]. When morning came, I said: "O Messenger of Allah, you did not cease reciting this verse until morning, bowing with it and prostrating with it." He said: "I asked my Lord for intercession for my nation, and He granted it to me. It is attainable, if Allah wills, for whoever does not associate anything with Allah."