Prayer: Doubt After Salaam
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1165
If a person doubts after the salām of the prayer whether or not his prayer was valid – for example, he doubts whether or not he performed rukūʿ, or after the salām of a four rakʿah prayer he doubts whether he performed four or five rakʿahs – he must dismiss his doubt. However, if both sides of his doubt are such that each possibility would mean his prayer is invalid – for example, after the salām of a four rakʿah prayer he doubts whether he performed three or five rakʿahs, his prayer is invalid.