Eating saḥūr is considered recommended, but if during eating saḥūr the fajr time arrives, one must throw up whatever food there is in their mouth. If they intentionally swallow some of that food after that, their fast is void and the kaffārah is due on them. Of course, it is better to make sure about the exact time of fajr before. Now, if they check the fajr time and thus become certain that the time has not arrived yet and thus continue eating saḥūr, however, they realize later that the fajr had already set out while they were eating, their fasting will be valid. A fasting person had better brush their teeth after eating saḥūr and before the fajr time. If they are sure that the pieces of food that are stuck between their teeth will be swallowed during the day, the obligatory precaution demands that they remove them. Otherwise, if by accident they swallow pieces of food later in the day, they must complete their fasting on that day and then fast another day as compensation for that day's fast. But if the taste or the smell of that food remains in the mouth, it will not invalidate fasting. Brushing the teeth, flossing or entering objects in the mouth does not invalidate fasting by themselves, but care should be taken that if an object is taken out of the mouth and then entered in it again with the moist of the mouth on it, it is impermissible to swallow one's saliva after that unless the moist on that object is so insignificant that it will disappear in to the saliva. When brushing the teeth with toothpaste, one should be careful to rinse out all of the toothpaste afterwards.