The Caesar said to Rabbi Yehoshua the son of Chananya: "Why does the food of Shabbat give off such a fragrance?"

He responded: "We have a spice, whose name is Shabbat, we put it in the dish and its fragrance spreads out."

He told him: "Give me some of it."

He replied: "This spice can only be useful to those who observe Shabbat and it is of no benefit to those who do not observe Shabbat."