Is it permissible to swallow saliva that has changed due to food residue after Suhoor, with the intention of moistening the throat and enjoying it? And is it obligatory to make up for the days on which this occurred due to ignorance of the ruling?

The well-known opinion in the Shafi'i madhhab is that swallowing saliva, if its taste or smell changes, does not invalidate the fast. However, if its color changes due to food, it does invalidate the fast, because the change in taste or smell occurs due to the proximity of food, while a change in color indicates its mixture [with the food].

Al-Nawawi mentioned that swallowing saliva does not invalidate the fast by consensus if it is in its usual state, but on the condition that the saliva is pure; if it mixes with something else and its color changes, then swallowing it invalidates the fast, whether the contaminant is pure or impure, because what is excused is the saliva due to necessity.

Some Shafi'i scholars held the view that swallowing saliva whose color has changed does not invalidate the fast, as long as no tangible substance from it has separated.

The more cautious approach is to avoid swallowing saliva whose color has changed entirely, as the color indicates the persistence of food particles within it. It is incumbent upon anyone who eats something that stains the saliva to thoroughly rinse their mouth.

If a fasting person is overcome by something that cannot be avoided, there is no blame on them. So, if food remains between one's teeth and saliva carries it unintentionally, one's fast is not invalidated if one is unable to distinguish and spit it out.

Sheikh Ibn Baz holds the view that swallowing ordinary saliva is permissible, but sputum (phlegm) from the chest or head must be expelled if it reaches the mouth, and if one intentionally swallows it, the fast is invalidated. If there is something else in the saliva, such as food remnants or blood, then if one is aware of it, one should not intentionally swallow it. However, if one is unaware and swallows one's saliva as usual, it does not harm the fast, because harm only occurs through intentional action.