(20) باب إِذَا صَلَّى قَاعِدًا ثُمَّ صَحَّ أَوْ وَجَدَ خِفَّةً تَمَّمَ مَا بَقِيَ
Narrated Aisha:
(the mother of the faithful believers) I never saw Allah's Messenger (ﷺ) offering the night prayer while sitting except in his old age and then he used to recite while sitting and whenever he wanted to bow he would get up and recite thirty or forty verses (while standing) and then bow.
Reference: Sahih al-Bukhari 1118
In-book reference: Book 18, Hadith 38
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 20, Hadith 219