Mishnayos Brachos Perek 8 Mishnah 3

מקנח ידיו במפה – From his first hand-washing and place it on the table and wipe his hands with it throughout from the filth of the cooked food; and he should not place it [the napkin] on the cushion on which he sits, as a preventive measure, lest the cushion becomes defiled in the first-degree, and the liquid comes in close contact with the napkin on account of the drying of the hands, and that liquid when it comes in contact with the cushion becomes [defiled] in the first-[degree], and the liquids become [defiled] in the first-[degree], and defile the hands when one wipes [one’s hands] with it continuously during the meal, but concerning the table [itself], there is no preventive measure made, for it is forbidden to use a table which is defiled in the second-degree. But the School of Hillel holds that it is permitted to use a table which is impure in the second-degree. Therefore, he should not leave the napkin on the table, lest the liquids become defiled that are on the napkin on account of the table and in turn would defile the food there, and if he leaves [the napkin] on the cushion, everyone should not suspect lest his hands became defiled; better that his hands become defiled – since they are not an essential principle from Torah law, since the washing of the hands for unconsecrated objects is not from the Torah and they don’t defile foods which have an essential principle from the Torah, for [something that is] unclean from the first-degree makes something unclean in the second-degree for unconsecrated objects from the Torah [perspective].