Muwatta Imam Malik (Riwayat Ibn al-Qasim)

Umm al-Mu'minin Sayyida Hafsa (may Allah be pleased with her) said: I never saw the Messenger of Allah (peace and blessings be upon him) performing voluntary prayers while sitting, until one year before his passing, he began to perform voluntary prayers while sitting. He would recite the surah with measured recitation (tarteel), so much so that due to his tarteel, that surah would become longer than a surah that was actually longer than it.

It is narrated from Umm al-Mu'minin Sayyidah Aisha (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to perform (nafl) prayer while sitting and would also recite while sitting. Then, when about thirty or forty verses remained from his recitation, he would stand up and recite, then bow (ruku') from the standing position, then prostrate (sajdah), and he would do the same in the second rak'ah.

And with the same chain of narration (it is narrated from Sayyida Aisha, may Allah be pleased with her) that she said she never saw the Messenger of Allah, peace and blessings be upon him, performing the night prayer sitting down, until when he became old, he would recite while sitting, then when he intended to bow (for ruku‘), he would stand and recite about thirty or forty verses, then he would bow.