The Book of Oaths and Vows
35/39. Chapter:
Saying: "If Allah Wills"
Sunan an-Nasai
أَخْبَرَنَا أَحْمَدُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنَا عَفَّانُ، قَالَ حَدَّثَنَا وُهَيْبٌ، قَالَ حَدَّثَنَا أَيُّوبُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " مَنْ حَلَفَ عَلَى يَمِينٍ فَقَالَ إِنْ شَاءَ اللَّهُ فَهُوَ بِالْخِيَارِ إِنْ شَاءَ أَمْضَى وَإِنْ شَاءَ تَرَكَ " .
It was narrated from Ibn 'Umar that the Messenger of Allah said: "Whoever swears an oath and says, 'If Allah wills,' then he has the choice: If he wishes, he may go ahead, and if he wishes he may not."
Reference : Sunan an-Nasa'i 3830In-book reference : Book 35, Hadith 70English translation : Vol. 4, Book 35, Hadith 3861