'Aayeshah Radiyallahu 'Anha says:
"Rasulullah Sallallahu 'Alayhi Wasallam Performed salaah (in old age) in a sitting posture (due to reciting lengthy portions) When about thirty or forty aayaat were left he stood up and recited (completed) these. He then performed the ruku' and sajdah. He did the same in the second rak'ah".
English reference: Book 39, Hadith 263
Arabic reference: Book 40, Hadith 279