Prayer: Swallowing Food Remnants, Doubting the Number of Rakʿahs, and Adding or Omitting Parts of the Prayer
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1141
If one swallows food that had remained in his mouth or in between his teeth while performing prayers, his prayer does not become invalid. Furthermore, there is no problem if a lump of sugar or sugar granules and suchlike remain in one’s mouth and gradually dissolve and are swallowed while one is performing prayers.
Eleventh: one has a doubt about the number of rakʿahs he has performed while performing a two rakʿah or three rakʿah prayer, or while performing the first two rakʿahs of a four rakʿah prayer, on condition that the doubt remains.
Twelfth: one intentionally or inadvertently does not perform a rukn of the prayer, or intentionally does not perform an obligatory component of the prayer that is not a rukn, or intentionally adds one of the parts of the prayer. Similarly, if one inadvertently adds a rukn like a rukūʿ or two sajdahs in the same rakʿah, his prayer becomes invalid based on obligatory precaution. As for inadvertently adding a takbīrat al‑iḥrām, this does not invalidate prayers.