"I heard the Messenger of Allah say this on this Minbar: 'It is not permissible for a woman who believes in Allah and His Messenger to mourn for anyone who dies for more than three days, except for a husband, (for whom the mourning period is) four months and ten days.'" (Using translation from Nasāʾī 3527)  

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ هَذَا عَلَى الْمِنْبَرِ «لَا يَحِلُّ لِامْرَأَةٍ تُؤْمِنُ بِاللهِ وَرَسُولِهِ أَنْ تُحِدَّ عَلَى مَيِّتٍ فَوْقَ ثَلَاثِ لَيَالٍ إِلَّا عَلَى زَوْجٍ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا»