זוהר שמות — דף פח ע”ב

Rabbi Abba rejoiced at each of the three Shabbat meals and gave each a distinct mystical designation: the meal of Atik Kadich, of the Holy One blessed be He, and of Zeir Anpin. Rabbi Shimon proclaimed to prepare the meal of the supreme faith, and at the third meal a verse from Isaiah was proclaimed in his honor. One who diminishes any meal causes a heavenly defect and proves himself unworthy of the King's sons. On festivals one must also gladden the poor, or face a harsh rebuke. But the rule for Shabbat differs.