Surat Al-Baqara (The Cow) - البقرة

لَّا يُؤَاخِذُكُمُ ٱللَّهُ بِٱللَّغْوِ فِىٓ أَيْمَٰنِكُمْ وَلَٰكِن يُؤَاخِذُكُم بِمَا كَسَبَتْ قُلُوبُكُمْ وَٱللَّهُ غَفُورٌ حَلِيمٌ ﴿٢٢٥﴾ لِّلَّذِينَ يُؤْلُونَ مِن نِّسَآئِهِمْ تَرَبُّصُ أَرْبَعَةِ أَشْهُرٍ فَإِن فَآءُو فَإِنَّ ٱللَّهَ غَفُورٌ رَّحِيمٌ﴿٢٢٦﴾

Allah does not call you to account for what is vain in your oaths, but He will call you to account for what your hearts have earned, and Allah is Forgiving, Forbearing. Those who swear that they will not go in to their wives should wait four months; so if they go back, then Allah is surely Forgiving, Merciful.