Sura al-Baqara 2:234

وَٱلَّذِينَ يُتَوَفَّوْنَ مِنكُمْ وَيَذَرُونَ أَزْوَٰجًا يَتَرَبَّصْنَ بِأَنفُسِهِنَّ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا فَإِذَا بَلَغْنَ أَجَلَهُنَّ فَلَا جُنَاحَ عَلَيْكُمْ فِيمَا فَعَلْنَ فِىٓ أَنفُسِهِنَّ بِٱلْمَعْرُوفِ وَٱللَّـهُ بِمَا تَعْمَلُونَ خَبِيرٌ

wa-lladhīna yutawaffawna minkum wa-yadharūna azwājan yatarabbaṣna bi-anfusihinna arbaʿata ashhurin wa-ʿashran fa-idhā balaghna ajalahunna fa-lā junāḥa ʿalaykum fī-mā faʿalna fī anfusihinna bil-maʿrūfi wallāhu bi-mā taʿmalūna khabīrun

If any of you die and leave widows behind, they shall wait concerning themselves four months and ten days: When they have fulfilled their term, there is no blame on you if they dispose of themselves in a just and reasonable manner. And Allah is well acquainted with what ye do.