Is there a hadith like “The leftover of a believer is a cure for the other believer.” ? Is an infidel’s leftover clean?

Is there a hadith like “The leftover of a believer is a cure for the other believer.” ? Is an infidel’s leftover clean?

Dear Brother / Sister,

We could not find the source of this hadith. However, those hadiths may not be applicable for all times and all things.

If a living being drinks from a bowl or a small pool, the remaining water is called the leftover.

Islamic jurisprudence says that a man’s leftover is clean. Man is a venerable being. Thus, no one’s leftover may be unclean even if he/she is a disbeliever. Provided that the food is lawful. The cleanliness of the liquid or food remnants depends on the eaters spit. Each human  being’s spit is clean. A disbeliever’s leftover is clean, too.
For instance, if a man drinks water from a glass, the glass is not considered to be unclean. Another person may use it without washing.
Moreover,in the hadiths, it is clearly stated that, one must not go to a place suffering from plague or epidemic diseases. Considering those two hadiths together, we come to the following conclusion:

It is not preferable to use the things that sick people use. However, it is not a sin to use the things that non-sick people use.

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