Many prophetic narrations mention half the reward for a person who performs sunnah or nafl ṣalāh.
As such, according to the most reliable opinion it is permissible to perform tarāwīḥ sitting down without an excuse is permissible (as standing in tarāwīḥ is not obligatory). However, performing while standing is mustaḥabb (recommended).
If, due to an excuse, all or some of the rakaʿāt’s (units) are performed while sitting, there will be no decrease in the reward.
Just how it is permissible to perform the entire ṣalāh sitting down, it is also permissible to begin the ṣalāh standing, and then sitting down in that same rakaʿāt (unit) or the second rakaʿāt (unit).
Similarly, it is permissible to begin tarāwīḥ while being seated, then standing up in that same rakaʿāt (unit) or the second rakaʿāt (unit).
If an individual remains seated during the qirā’ah (recitation), and then stands to perform rukū (bowing), it is permissible and transmitted from the Messenger of Allāh (may Allah bless him and grant him peace).
(Adapted from Tarāwīḥ ke Aham Masā’il by Muftī Muhammad Riḍwan. Published by Kutub Khāna Idāra Gufrān, Rawalpindi.)
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