Sunan an-Nasa'i 1653
سنن النسائي#1653SahihIt was narrated from Al-Aswad, that Umm Salamah said:"The Messenger of Allah (ﷺ) did not pass away until most of his prayers were offered sitting down, except for the obligatory prayers
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih Lighairihi
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 20:56