Sayyiduna al-Nu'man bin Bashir (may Allah be pleased with him) narrates from Sayyiduna Mu'awiyah bin Abi Sufyan (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, Allah, the Mighty and Majestic, has placed the truth upon the tongue and the heart of Umar."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16756