The Chapters on Expiation
11/6. Chapter:
Uttering the exception when swearing
Sunan Ibn Majah
حَدَّثَنَا مُحَمَّدُ بْنُ زِيَادٍ، حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ، عَنْ أَيُّوبَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " مَنْ حَلَفَ وَاسْتَثْنَى إِنْ شَاءَ رَجَعَ وَإِنْ شَاءَ تَرَكَ غَيْرُ حَانِثٍ " .
It was narrated from Ibn 'Umar that the Messenger of Allah (ﷺ) said: "Whoever swears an oath and says In sha' Allah, if he wishes he may go ahead and if he wishes he may not, without having broken his oath."
Reference : Sunan Ibn Majah 2105In-book reference : Book 11, Hadith 16English translation : Vol. 3, Book 11, Hadith 2105