Prayer: Realising Private Parts are Visible
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 779
If someone realises during his prayers that his private parts are visible, he must cover them but it is not necessary for him to repeat his prayers. However, the obligatory precaution is that while he realises his private parts are visible, he must not continue with any component of the prayer. If he realises after his prayer that during the prayer his private parts were visible, his prayer is valid.