Prayer: Intentionally Not Covering Private Parts
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 778
When performing prayers, if one intentionally does not cover his private parts,[1] his prayers are invalid. If he does this on account of not knowing the ruling, then in the event that he was negligent in not learning the ruling, he must, based on obligatory precaution, perform the prayers again.
-Ayatullah Sistani, Practical Laws of Islam, Prayer (Salah)
1
With regard to a woman, ‘private parts’ in this and in subsequent rulings pertaining to covering the body in prayers refers to all the parts of the body that a woman must cover in prayers; i.e. her entire body – apart from her face, her hands below the wrists, and her feet below the ankles (Tawḍīḥ al‑Masāʾil‑i Jāmiʿ, vol. 1, p. 288, Ruling 933).