Surat Al-Baqara (The Cow) - البقرة

وَٱلَّذِينَ يُتَوَفَّوْنَ مِنكُمْ وَيَذَرُونَ أَزْوَٰجًا يَتَرَبَّصْنَ بِأَنفُسِهِنَّ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا فَإِذَا بَلَغْنَ أَجَلَهُنَّ فَلَا جُنَاحَ عَلَيْكُمْ فِيمَا فَعَلْنَ فِىٓ أَنفُسِهِنَّ بِٱلْمَعْرُوفِ وَٱللَّهُ بِمَا تَعْمَلُونَ خَبِيرٌ ﴿٢٣٤﴾

And (as for) those of you who die and leave wives behind, they should keep themselves in waiting for four months and ten days; then when they have fully attained their term, there is no blame on you for what they do for themselves in a lawful manner; and Allah is aware of what you do.