The Grand Ayatollah Khamenei answered a question about Salaat.
Question: What is the duty of a person who unintentionally starts performing Isha Salaat/Salaah before Maqrib/Maghrib, and during the Salaat realizes that has made a mistake?
The Grand Ayatollah Khamenei: If has not started the fourth Roku, must change the intention (Niyyah) to Salaat of Maqrib and complete the Salaat, and then perform Salaat of Isha. But if has started the fourth Roku, according to precaution must complete the Salaat, and then perform Salaats of Maqrib and Isha.
