Leviticus 15:8

And if he that hath the issue spit upon him that is clean
Not purposely, which is not usual for a man to do, and whenever it is done, nothing is more affronting; but accidentally, when, as Aben Ezra expresses it, he spreads his spittle, and it falls upon a clean person; and under this, as Gersom observes, is comprehended whatever is brought up by coughing, as phlegm, or flows from the nose, or is pressed out of it; and so Maimonides ^F26: and this may denote all corrupt communication which proceeds out of the mouth of evil men, whether immoral or heretical, which not only defiles the man himself, but those he converses with; for evil communication corrupts good manners:

then he shall wash his clothes
as in the foregoing instances. (See Gill on Leviticus 15:5).