The Ruling on Praying in a Flimsy or Transparent Garment
Does a clear, thin garment cover the Awrah or not? And is prayer of a Muslim who wears it correct or not?
If the above-mentioned garment does not cover the skin due to its transparency or thinness, then it is not permissible for a man to pray in it, unless he has some other garments which cover up what is between the navel and the knees ... As for the women, her prayer will not be acceptable in such a garment, unless she wears something underneath it which covers her whole body. As for the short pants that are worn under the aforementioned garment, they are not sufficient, and a man who prays in such clothes must wear a vest or something else which covers the shoulders, or one of them, according to the Hadith of the Prophet (sallallaahu alaihi wa sallam) which states: None of you should pray in one garment which does not cover anything of his shoulders. 
 Muslim no. 516 and Abu Dawud no. 626.
Shaykh `Abdul-`Azeez Bin Baz
Fatawa Islamiyah Vol. 2 Page 171