The Ruling on Praying in a Transparent Garment

This is a message we received from the questioner Sharaf al-Din 'Abdullah al-Sayani, from the sons of the Yemen Arab Republic. He says in his message: There are some people who pray in a very light garment and without long trousers; rather, they wear very small trousers. Is their prayer valid, and what do you advise them?
Answer: If the one praying is a man, it is obligatory for him to cover what is between the navel and the knee, and to have on covering trousers, or a covering shirt. If his garment is light and reveals the thigh—the flesh of the thigh—so that it is known whether it is black or red, then this clothing does not cover and is not sufficient, and the prayer is not valid with it, as if he were uncovered.
As for if the clothing covers the thighs and the private parts, but it is light and it covers, then there is no harm. Or if he has on sufficient trousers that cover what is between the navel and the knee, then there is no harm. Or a covering waistcloth.
As for the woman, it is obligatory for her to cover her entire body in prayer. It is obligatory for her clothing to be covering and thick, so that her body is not seen; rather, she reveals only her face in prayer. And if she reveals her hands, there is no harm; but it is better to cover the hands as well. It is not permissible for her to pray in light garments through which her flesh is seen and it is known whether it is red or black. The ruling on this is the ruling of being naked; her prayer is not valid. Yes.