Leviticus 15:6
And he that sitteth on any thing whereon he sat that hath the issue shall wash his clothes, and bathe himself in water, and be unclean until the even. And he that sitteth on any thing whereon he sat that hath the issue shall wash his clothes, and bathe himself in water, and be unclean until the even.
Anyone who sits on anything on which a man with a discharge has sat must wash his clothes and bathe in water and remains unclean until evening. Indirect contact through objects and clothing associated with bodily discharge conveys temporary ceremonial uncleanness, and objects and clothing are treated as possible means of contamination that require washing and cleansing after contact.
The requirement belongs to regulations showing how thoroughly rules concerning contaminating conditions were enforced. Related instructions required a person with such personal uncleanness to remain outside the camp until evening and to cleanse himself and his clothing before returning.
These requirements also served as sanitary measures that kept uncleanness from contributing to disease.