Mishkat al-Masabih
Mishkat al-Masabih 3415
Section 1
Arabic hadith text
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَمِينُكَ عَلَى مَا يُصَدِّقُكَ عَلَيْهِ صَاحبك» . رَوَاهُ مُسلم
Translation
He reported God’s Messenger as saying, "Your oath should be about something regarding which your companion will believe you.” Muslim transmitted it.