Musnad Ahmad 27:1247

Abu Amir narrated to us, Kharijah ibn Abdullah al-Ansari narrated to us, from Nafi’, from Ibn Umar, from the Prophet (peace and blessings of Allah be upon him), who said: "Indeed, Allah the Almighty and Majestic placed the truth upon the heart of Umar and his tongue." Ibn Umar said: "No matter ever befell the people such that they spoke about it, and Umar ibn al-Khattab spoke about it—or he said: 'Umar said'—except that the Quran was revealed in accordance with what Umar had said."