Kharashah bin al-Hurr (may Allah have mercy on him) narrates from Sayyiduna Abu Dharr (may Allah be pleased with him), who said: I heard the Messenger of Allah (peace and blessings be upon him) one night while he was praying and repeating a single verse over and over until morning came. He bowed and prostrated with it, and the verse is: "If You punish them, they are Your servants" [Surah al-Ma'idah: 118]. I said: "O Messenger of Allah, you kept repeating one verse until morning came." He (peace and blessings be upon him) said: "I asked my Lord for intercession for my Ummah, and this intercession will be for whoever has not associated partners with Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4717