The Prophet ﷺ said: If anyone says when swearing an oath: "If Allah wills," he makes an exception.  

النَّبِيَّ ﷺ قَالَ مَنْ حَلَفَ عَلَى يَمِينٍ فَقَالَ إِنْ شَاءَ اللَّهُ فَقَدِ اسْتَثْنَى  

The Prophet ﷺ said: If anyone swears an oath and makes an exception, he may fulfil it if he wishes and break it if he wishes without any accountability for breaking.  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ حَلَفَ فَاسْتَثْنَى فَإِنْ شَاءَ رَجَعَ وَإِنْ شَاءَ تَرَكَ غَيْرَ حِنْثٍ