Bulugh al-Maram, Book 13, Hadith 3 (In-Book)

Narrated Abu Hurairah (RA): Allah's Messenger said: "Your oath will be about that matter which your adversary has required you to swear about so that he will believe you." In another narration: "An oath is to be interpreted according to the intention of the one who requested it (Al-Mustahlif)." [Muslim reported both narrations].

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ " يَمِينُكَ عَلَى مَا يُصَدِّقُكَ بِهِ صَاحِبُكَ" } وَفِي رِوَايَةٍ: { "اَلْيَمِينُ عَلَى نِيَّةِ اَلْمُسْتَحْلِفِ" } أَخْرَجَهُمَا مُسْلِمٌ 1‏.‏ ‏1 ‏- صحيح رواه مسلم ( 1653 )‏.‏

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also referenced under: Book 13, Hadith 1376 (English)