"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."
Reference: Jami` at-Tirmidhi 374 In-book : Book 2, Hadith 226 English translation : Vol. 1, Book 2, Hadith 374
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