It was narrated that 'Abdullah bin 'Amr said:
"I heard the Messenger of Allah say: 'There is no one on earth, or under the sky, who speaks more truthfully than Abu Dharr.'" (FR)
English reference (FR): Vol. 1, Book 1, Hadith 156 (FR)
Arabic reference (FR): Book 1, Hadith 161 (FR)