A: Haamidaw wa Musalliyaa
As a general rule, it is makruh (disliked) to wear in salah any attire which a person of sound religious disposition will not wear in a respectable gathering or in front of a respectable person. This is so because in salah a person is standing before the Lord of both worlds. Thus short sleeve shirts are not an appropriate form of dress for salah.
In this regard we should remember the command of Allah:
خُذُواْ زِينَتَكُمْ عِندَ كُلِّ مَسْجِدٍ
”Wear your beautiful apparel at every time and place of prayer.” [Al-a’raf, 7:31]
And Allah Ta'ala Knows Best
Shafiq Jakhura (Mufti)