وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَمِينُكَ عَلَى مَا يُصَدِّقُكَ عَلَيْهِ صَاحبك»
He reported God’s Messenger as saying, “Your oath should be about something regarding which your companion will believe you.”
Mishkat al-Masabih 3282, Book 16, Oaths and Vows, Hadith 10. 1 min read