The Satrul Aurah (area of the body which must always be covered) for a man is as follows,
و عورة الرجل ما تحت السرة الى الركبة
“the Aurah for a male is from below his navel until the knees (i.e. including the knees)”
(Al-Hidaaya, Vol. 1, pg. 92)
If one-fourth of the body part (i.e. internal gluteal cleft) which must be covered in Salaah is exposed equal to the duration of one Rukn, meaning the time it takes to say Subhanallah thrice, the Salaah will not be valid, even if it was exposed unintentionally.
(Raddul Muhtaar, Vol. 1, pg. 408)
It is incumbent upon Muslims to use clothing that does not expose the Satrul Aurah. In Salaah, one should take care in dressing according to the desires of the Shariah as the Holy Quraan states,
خُذُوۡا زِيۡنَتَكُمۡ عِنۡدَ كُلِّ مَسۡجِدٍ
“adorn yourself appropriately at the time of Salaah”
(Surah A’raaf, Verse 31)
Therefore, those skinny fitting pants, jeans, shirts or t-shirts which expose this area of the body when one goes into Ruku and Sajda must not be used in Salaah.
One can use a jubba or another piece of clothing to cover the shirt or jeans for the Salaah to be valid.
And Allah and His Rasool know best.
Islamic Lifestyle Solutions