It is narrated from Amr bin Maymun al-Awdi that when Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) was stabbed, the people put Abd al-Rahman bin Awf (may Allah be pleased with him) forward. He led the people in the Fajr prayer and recited in it: "When the victory of Allah has come" [Surah al-Nasr: 1] and "Indeed, We have granted you al-Kawthar" [Surah al-Kawthar: 1].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4023