זוהר בראשית — דף ריג ע”א

When the Holy One blessed be He wished to liberate Israel from Egypt, He struck Pharaoh and Egypt with plagues. The consolation is that the Other Side rules only by permission. The plagues — each one is an emissary of holiness fulfilling its mission. Pharaoh hardened his heart at each plague until every bone of the evil palace was broken.