Does swallowing saliva that has left the mouth invalidate the fast?
General Chapter
Al-Mughni
Book of Fasting
Primary text
If a person's saliva leaves their mouth onto their clothing, fingers, or lips, and then returns to be swallowed, it invalidates the fast. Similarly, swallowing another person's saliva breaks the fast. This is because the saliva is being swallowed from outside the mouth, analogous to swallowing something else entirely.
Supporting text
The view that it does not invalidate the fast is supported by the reasoning that the actual separation and descent of that moisture into the throat is not definitively established, similar to rinsing the mouth (madmadah) or using a wet siwak (miswak).