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.  

عَنِ النَّبِيِّ ﷺ أَنَّهُ رَخَّصَ لِلْمُتَوَفَّى عَنْهَا عِنْدَ طُهْرِهَا فِي الْقُسْطِ وَالأَظْفَارِ