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.
Sunan an-Nasa'i Book 27, Hadith 156
← Previous Hadith "A woman came to the Prophet and asked him about that, and he said: 'During the Jahiliyyah, if her husband died, one of you would stay (in mourning) for a year, then she would throw a piece of dung then come out. Rather it (the mourning period) is four months and ten days, until the term prescribed is fulfilled.'"

Sunan an-Nasa'i Book 27, Hadith 155 Next Hadith → "And those of you who die and leave behind wives should bequeath for their wives a year's maintenance and residence without turning them out." This was abrogated by the Verse on inheritance, which allocated to her one-quarter or one-eighth. And the appointed time ('Iddah) of one year was abrogated and replaced with the ('Iddah) term of four months and ten days.

Sunan an-Nasa'i Book 27, Hadith 157