´It was narrated that 'Abdullah bin 'Amr said:` "I saw the Prophet (ﷺ) praying sitting down and I said: 'I was told that you said that the prayer of one who is sitting down is worth half of the prayer of the one who is standing up.' He said: 'Yes indeed, but I am not like any one of you.'"
Explanation & Benefits
Hafiz Muhammad Ameen
1660. Commentary:
➊ "I am not like you"—that is, I receive the full reward even when I pray sitting, and this is a special distinction of the Messenger of Allah (sallallahu alayhi wa sallam). This meaning may also be intended: that I pray sitting due to an excuse, and half the reward is for the one who prays voluntary prayers (nawafil) sitting without an excuse. Furthermore, in your youth, you used to perform voluntary prayers standing. If a person performed a good deed in his youth but, due to old age, is unable to do so, then Allah, out of His mercy, grants him the full reward.
➋ It is permissible to perform voluntary prayers (nawafil) sitting even when one has the ability to stand, but remember that the reward will be half.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 1660