Hadith 12:19
Ibn ‘Umar reported God’s Messenger as stating that if anyone says when swearing an oath, “If God will”, he is not held accountable if he breaks it. Tirmidhi, Abu Dawud, Nasa’i, Ibn Majah and Darimi transmitted it, but Tirmidhi mentioned a number who traced it no farther back than Ibn ‘Umar.
وَعَنِ ابْنِ عُمَرَ أَنَّ رَسُولَ اللَّهِ صَلَّى الله ليه وَسَلَّمَ قَالَ: " مَنْ حَلَفَ عَلَى يَمِينٍ فَقَالَ: إِنْ شَاءَ اللَّهُ فَلَا حِنْثَ عَلَيْهِ " رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالنَّسَائِيُّ وَابْنُ مَاجَهْ وَالدَّارِمِيُّ وَذَكَرَ التِّرْمِذِيُّ جَمَاعَةً وَقَفُوهُ عَلَى ابْنِ عُمَرَ
Original Reference: Mishkat al-Masabih 3424