"It is not permissible for a woman who believes in Allah and the Last Day to mourn for more than three days, except for her husband." (Using translation from Nasāʾī 3526)
عَنِ النَّبِيِّ ﷺ قَالَ «لَا يَحِلُّ لِامْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الْآخِرِ أَوْ تُؤْمِنُ بِاللَّهِ أَنْ تَحِدَّ عَلَى أَحَدٍ فَوْقَ ثَلَاثَةِ أَيَّامٍ إِلَّا عَلَى زَوْجِهَا»