Mishnah — Seder Moed, Tractate ShabbatChapter 22
“ Mishnah 4 One may put cooked victuals into a cave (or cellar) for the purpose of preserving them; also put clean water (contained in a vessel) into water that is not drinkable, in order to keep it (the former) cool; likewise cold water (in a vessel) into hot water, in order to warm the former. One whose clothes have dropped into the water while on the road, may unhesitatingly go on with them. ”
