عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ مَنْ حَلَفَ فَقَالَ إِنْ شَاءَ اللَّهُ لَمْ يَحْنَثْ
It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Whoever swears an oath and says "Insha'Allah" (if Allah wills), then he will not be held accountable for breaking it.