Sura al-Baqara 2:226

لِّلَّذِينَ يُؤْلُونَ مِن نِّسَآئِهِمْ تَرَبُّصُ أَرْبَعَةِ أَشْهُرٍ فَإِن فَآءُو فَإِنَّ ٱللَّـهَ غَفُورٌ رَّحِيمٌ

li-lladhīna yuʾlūna min nisāʾihim tarabbuṣu arbaʿati ashhurin fa-in fāʾū fa-inna allāha ghafūrun raḥīmun

For those who take an oath for abstention from their wives, a waiting for four months is ordained; if then they return, Allah is Oft-forgiving, Most Merciful.