משנה אויף ויקרא 15:12

One who touches a zav, or whom a zav touches, who moves a zav or whom a zav moves, defiles by contact food and liquids and vessels that are rinsed, but not by carrying. A general principle was stated by Rabbi Joshua: anyone that defile garments while still in contact [with their source of uncleanness] also defiles foods and liquids so as to become [unclean] in the first grade, and the hands so that they become [unclean] in the second grade; but they do not defile people or earthenware vessels. After they separated from their source of uncleanness they defile liquids so as to become [unclean] in the first grade, and food and the hands so that they become [unclean] in the second grade, but they do not defile garments.