Sunan an-Nasa'i, Book 27, Hadith 156 (In-Book) ⓘ
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.
أَخْبَرَنَا الْعَبَّاسُ بْنُ مُحَمَّدٍ، - هُوَ الدُّورِيُّ - قَالَ حَدَّثَنَا الأَسْوَدُ بْنُ عَامِرٍ، عَنْ زَائِدَةَ، عَنْ هِشَامٍ، عَنْ حَفْصَةَ، عَنْ أُمِّ عَطِيَّةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ رَخَّصَ لِلْمُتَوَفَّى عَنْهَا عِنْدَ طُهْرِهَا فِي الْقُسْطِ وَالأَظْفَارِ .
also referenced under: Hadith 3542 (Reference) & Volume 4, Book 27, Hadith 3572 (DarusSalam)