Is vomit and water discharged from the mouth during sleep impure?

The majority of scholars hold that vomit is impure in all cases, while the Malikis restricted its impurity to that which has changed from food. As for the water that comes out of a sleeping person's mouth: if it is saliva, it is pure; but if it is from the stomach, it is impure, distinguished by its yellow color and foul odor. If this affects a person constantly, it is excused to avoid hardship.