Prayer: Changing Intention From a Precautionary Prayer
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 748
If a person performs a prayer and then performs it again as a precautionary measure, and during the prayer he remembers that he has not performed the prayer that was necessary for him to perform before it, he cannot change his intention to that prayer. For example, if when he performs the ʿaṣr prayer as a precautionary measure, he remembers he has not performed the ẓuhr prayer, he cannot change his intention to the ẓuhr prayer.