Prayer: Validity of Prayers Started Early Due to Mistake
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 731
If, through one of the ways mentioned previously, it becomes established for someone that the time for prayers has set in and he starts to perform his prayer, and during the prayer he realises that the time has not yet set in, his prayer is invalid. The same applies if he realises after the prayer that he performed the entire prayer before the time had set in. However, if during the prayer he realises that the time has set in, or if he realises after the prayer that during the prayer the time had set in, his prayer is valid.