Prayer: Forgetting or Not Knowing Clothing is Usurped
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 804
If someone does not know his clothing is usurped or forgets that it is and performs prayers with it, his prayers are valid. However, if someone usurps some clothing himself and forgets that he has usurped it and performs prayers with it, then based on obligatory precaution, his prayers are invalid.