'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". Commentary A group among the 'Ulama have stated that it is not jaa-iz for a person performing salaah in a sitting posture to stand up - then perform the ruku'and sajdah. The majority of the 'ulama including the four a-immah say it is jaa-iz (permissible) to do so. Likewise it is also jaa-iz to stand and perform these. This applies only to nafl salaah. It is not permissible for the able-bodied who can stand, to sit and perform the fard salaah. [+] [Tirmidhi 039:016 (263)]