Mishkat al-Masabih 30 Fine Qualities كتاب المناقب 96

وَعَنْ أَبِي سَهْلَةَ قَالَ: قَالَ لِي عُثْمَانُ يَوْمَ الدَّارِ: أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَدْ عَهِدَ إِلَيَّ عَهْدًا وَأَنَا صَابِرٌ عَلَيْهِ. رَوَاهُ التِّرْمِذِيُّ وَقَالَ: هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ

Abu Sahla told that `Uthman said to him on the day of the house, “God’s messenger made a covenant with me and I shall show endurance in adhering to it.” Tirmidhi transmitted it, saying this is a hasan sahih tradition.