Jami` at-Tirmidhi 374
جامع الترمذي#374SahihAishah narrated:"The Prophet (S) would perform Salat while sitting. And he would recite while sitting. When about thirty or forty Ayah of his recitation remained he would standup and recite while he was standing, then he would bow and prostrate. Then he would do the same in the second Rak'ah
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 2:226