It was narrated from Hafsah, from Umm 'Atiyyah, from the Prophet, that he granted a concession to the woman whose husband has died, allowing her to use Qust and Azfar when purifying herself following her menses. (Using translation from Nasāʾī 3542)  

عَنِ النَّبِيِّ ﷺ أَنَّهُ «رَخَّصَ لِلْمُتَوَفَّى عَنْهَا زَوْجُهَا عِنْدَ طُهْرِهَا فِي الْقُسْطِ وَالْأَظْفَارِ»