Mishkat al-Masabih 30 Fine Qualities كتاب المناقب 261

وَعنهُ قا ل: اسْتَغْفَرَ لِي رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ خمْسا وَعشْرين مرّة. رَوَاهُ التِّرْمِذِيّ

He told that God’s messenger asked forgiveness for him twenty-five times. Tirmidhi transmitted it.