It was narrated that Abu Dharr said:
"I heard the Messenger of Allah say: 'Allah has placed the truth on the tongue of 'Umar, and he speaks with that (truth).'" (JA)
English reference (JA): Vol. 1, Book 1, Hadith 108 (JA)
Arabic reference (JA): Book 1, Hadith 113 (JA)