מדרש על ויקרא 17:16

13) We find, then, that if one were eating the neveilah of a clean bird, one of his hands on an (earthen) stove, and the other on his neighbor, both are tahor. (Vayikra 17:16) "And if he does not wash … then he shall bear his sin": I might think that for failure to wash his clothes he incurs the punishment of kareth; it is, therefore, written "not bathe his flesh, then he shall bear his sin — For failure to bathe his body the punishment is kareth, but for failure to wash his clothes, it is forty lashes.