Sunan Ibn Majah, Hadith 108 ⓘ
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).'"
حَدَّثَنَا أَبُو سَلَمَةَ، يَحْيَى بْنُ خَلَفٍ حَدَّثَنَا عَبْدُ الأَعْلَى، عَنْ مُحَمَّدِ بْنِ إِسْحَاقَ، عَنْ مَكْحُولٍ، عَنْ غُضَيْفِ بْنِ الْحَارِثِ، عَنْ أَبِي ذَرٍّ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ يَقُولُ " إِنَّ اللَّهَ وَضَعَ الْحَقَّ عَلَى لِسَانِ عُمَرَ يَقُولُ بِهِ " .
also referenced under: Book 1, Hadith 113 (In-Book) & Volume 1, Book 1, Hadith 108 (DarusSalam)