Weak
graded by Al-Albani
Mishkat al-Masabih 3423
Narrator:Abu Hurayrah
وَعَن أبي هُرَيْرَة قَالَ: كَانَتْ يَمِينُ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا حَلَفَ: «لَا وَأَسْتَغْفِرُ اللَّهَ» . رَوَاهُ أَبُو دَاوُد وَابْن مَاجَه
Abu Huraira said that when God’s Messenger swore an oath it was, “No, and I ask forgiveness of God.” Abu Dawud and Ibn Majah transmitted it.
Cited in Mishkat al-Masabih (No. 3423).