The Prophet ﷺ used to pray while seated, reciting in that position. When about thirty or forty verses of his recitation remained, he would stand up and recite them while standing, then bow and prostrate. He would do the same in the second rakah.
حدثنا القعنبي عن مالك عن عبد الله بن يزيد وأبي النضر عن أبي سلمة بن عبد الرحمن
أن النبي ﷺ كان يصلي جالسا فيقرأ وهو جالس وإذا بقي من قراءته قدر ما يكون ثلاثين أو أربعين آية قام فقرأها وهو قائم ثم ركع ثم سجد ثم يفعل في الركعة الثانية مثل ذلك
Bukhari narrated it in "Shortening the Prayer," chapter "If he prayed sitting, then recovered or felt lighter," etc., no. 1119, and Muslim in "The Prayer of Travelers," chapter "The permissibility of voluntary prayer standing and sitting," etc., no. 731, from the hadith of Malik through him, and it is in Muwatta (Yahya version) 1/138.