Does the prayer and fasting become invalidated if the worshiper swallows some of his saliva that came out to the corner of his mouth and then re-entered his mouth, knowing that it always comes out, and it is difficult to wipe it due to scrupulosity?

Leave off these whisperings (waswas), and pay them no mind. Proceed with your prayer and recitation without being concerned by them. Swallowing your saliva during prayer does not harm you, whether it accumulated inside the mouth or was between the lips. Ignore scrutinizing this matter and searching into it, for the best cure for whisperings is to disregard them and not pay them any attention.