Sunan an-Nasa'i 1646
سنن النسائي#1646SahihIt was narrated that 'Aishah said:"The Messenger of Allah (ﷺ) used to pray for a long time at night. If he started to pray standing, he would bow standing and if he started to pray sitting, he would bow sitting
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih Muslim
In-book reference: 20:49