وَالَّذِينَ يُتَوَفَّوْنَ مِنكُمْ وَيَذَرُونَ أَزْوَاجًا يَتَرَبَّصْنَ بِأَنفُسِهِنَّ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا فَإِذَا بَلَغْنَ أَجَلَهُنَّ فَلاَ جُنَاحَ عَلَيْكُمْ فِيمَا فَعَلْنَ فِي أَنفُسِهِنَّ بِالْمَعْرُوفِ وَاللّهُ بِمَا تَعْمَلُونَ خَبِيرٌ
﴿٢٣٤﴾
سورة البقرة
(2/234) The wives of those who are made to die and leave them behind, should keep themselves in waiting for four months and ten days; then when they have fully attained their term, there is no sin on you for what they do for themselves in a lawful manner (on a reasonable basis, bi’l ma’rûf) and Allah is Well-Acquainted with what you do.
Surah Al-Baqarah