Tractate Oholot - Chapter 15 - Mishnah 5 אהלות פרק ט״ו משנה ה׳

[In the case where] it was partitioned off from the floor: If there is uncleanness beneath the partition, vessels in the house become unclean. [In the case where] the uncleanness is in the house, vessels beneath the partition, If there is a space there of one cubic hand breadth, remain clean; But if not, they become unclean, since the floor of the house is reckoned as the house even to the nethermost deep.