Answered by Shaykh Faraz Rabbani
If one finds in his prayer that there is some small morsel of food in his mouth what should he do? What happens if it is accidentally swallowed?
Walaikum assalam wa rahmatullah,
Spit it out onto one’s sleeve or napkin.
1. If one swallows less than a dried chickpea worth of food from within the mouth, it does NOT break the prayer. More than that does.
2. If one swallows even a little food or liquid from outside the mouth, it invalidates the prayer.
3. If food remains within the mouth, it does not affect the validity of the prayer.
[from: Maraqi, Durr]
Wassalam,
Faraz Rabbani