Exodus 9:29
And Moses said unto him, As soon as I am gone out of the city, I will spread abroad my hands unto the LORD; and the thunder shall cease, neither shall there be any more hail; that thou mayest know how that the earth is the LORD’s. And Moses said unto him, As soon as I am gone out of the city, I will spread abroad my hands unto the LORD; and the thunder shall cease, neither shall there be any more hail; that thou mayest know how that the earth is the LORD’s.
Pharaoh admitted he had sinned and that the Lord was righteous, and he together with his people pleaded for intercession that the storm might stop. In reply Moses pledged that the moment he left the city he would stretch out his hands to the Lord in prayer, and the thunder would end and hail fall no more. He gave this pledge in order that Pharaoh might learn that the earth is the Lord's, subject to His power and command over the land and its forces.
Even while promising, Moses understood that Pharaoh and his servants did not yet truly revere God, and that their admission of wrong and offer to release Israel sprang from terror rather than enduring change of heart. The judgments had been foretold in advance so that their exact timing would prove they were not accidents, and at Moses' prayer the tempest listened to God's voice and halted, revealing His mastery over the elements and His care to safeguard His messenger. Yet once relief came Pharaoh would not free Israel, for persistent resistance had hardened him until his entire being stood in rebellion against the displays of divine power.