Swallowing bits of food that are left in the mouth during the day
Praise be to Allah,
Rulings on a person who swallows something that is stuck between his teeth.
The scholars agree that if any food particles is stuck between tooth of a person and he swallows it unintentionally, then fast is valid. This applies to the case when the food particles are too small and it mixes with the saliva.
However, when the food particles are big enough and he deliberately swallows it, then it breaks his fast. But if the food particles has already reached his throat and he cannot expel it, then there is no sin on him if he swallows it and his fast remains valid.
Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni, 3/260:
If a person has food between his teeth, one of the following two scenarios must apply:
1 – It is a small amount that he cannot spit out, so he swallows it. This does not invalidate his fast, because it cannot be avoided. It is like saliva. Ibn al-Mundhir said: The scholars are unanimously agreed on that.
2 – It is a large amount and he can spit it out. If he spits it out there is no sin on him, but if he swallows it deliberately, his fast is invalidated according to the majority of scholars, because he has swallowed food that he could have spat out willingly when he is mindful of his fast. So this breaks the fast just as if he deliberately started eating. End quote.[i]
Shaykh al Munajjid[ii] further elaborates:
If a person unintentionally swallows something that is stuck between his teeth, or if it is so small that he could not tell it was there or spit it out, this is counted as being part of his saliva and it does not break his fast. But if it is big enough to spit out, he should spit it out. If he spits it out, this is OK, but if he swallows it, this breaks his fast. If it can be diluted in the mouth, in whole or in part, and it has an added taste or sweetness, it is haraam for him to chew it. If any of this substance reaches the throat, this breaks the fast. If a person spits out water after rinsing his mouth, his fast is not affected by any moisture or wetness that is left behind, because he cannot help it[iii].
View of sheikh Salih Al Fawzan:
This will not nullify his fast as the mouth is still considered a part of the external bodily system. If he swallows the food deliberately however, his fast is nullified[iv].
The Hanafi view
If the food between the teeth was there before fajr time, and the amount swallowed was less than the extent of a small chickpea, the fast is not invalidated.
However, if it entered the mouth after fajr time, or if the amount swallowed was more than the extent of a small chickpea, then the fast is invalidated[v].
[i] https://islamqa.info/en/answers/78438/swallowing-bits-of-food-that-are-left-in-the-mouth-during-the-day
[ii] Founder and general supervisor of Islam Questions & Answers website (islamqa.com) in 1996 CE.
[iii] Salih al Munajjid 70 Matters Related to Fasting- PDF, page 26.
[iv] Salih Al Fawzan, A Commentary on
Zad al-Mustaqni’ Imam al-Hajjawi’s (d.968 h .) Classical Guide to the Hanbali Madhab, pdf- page 595]