Surah 26. Ash-Shuara, Ayah 29

In the religion of ancient Egypt, the king (or "Pharaoh", as each of the rulers was styled) represented an incarnation of the divine principle, and was considered to be a god in his own right. Hence, a challenge to his divinity implied a challenge to the prevalent religious system as a whole.

Now we come to the crisis. Pharaoh threatens Moses with prison for treason. Moses remains calm and still argues: "What if I show you a miracle? Will it convince you that I am not mad, and that I have behind me the Lord of all the Worlds?"