Leviticus 5:2-3

2“Or if a person touches any unclean thing—whether it is the carcass of an unclean animal or the carcass of unclean livestock or the carcass of unclean creeping things, though it is hidden from him, still he is unclean and he will be guilty.

3“Or if he touches some human uncleanness, whatever his filth is by which he is unclean, though it is hidden from him, when he knows of it, then he will be guilty.