If MAKROOH, please give reference of any fiqh or hadith.
Ref. No. 903/41-11B
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
One should wear proper clothing while praying namaz. Allah says in the Quran: O Children of Adam! Take your adornment while praying. It means one should dress up for namaz and adopt clothing that is interpreted by Islamic scholars as being in accordance with the teachings of Islam.
Secondly, wearing a garment against its proper form is also disliked. Therefore, praying in half sleeved garment without any proper reason is Makrooh (disliked).
(و) كره (كفه) أي رفعه ولو لتراب كمشمر كم أو ذيل (الدرالمختار 1/640)
And Allah knows best
Darul Uloom Waqf Deoband
This answer was collected from the official website of Darul Uloom Deoband Waqf. The institution is based in India and the answers are provided in accordance to the Hanafi Fiqh.