He reported God’s Messenger as saying, "Your oath should be about something regarding which your companion will believe you.” Muslim transmitted it.

وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَمِينُكَ عَلَى مَا يُصَدِّقُكَ عَلَيْهِ صَاحبك» . رَوَاهُ مُسلم