Exodo  17, 6-4

Behold, I will stand before thee there upon the rock in Horeb; and thou shalt smite the rock, and there shall come water out of it, that the people may drink. And Moses did so in the sight of the elders of Israel. And Moses lifted up his hand, and with his rod he smote the rock twice: and the water came out abundantly, and the congregation drank, and their beasts also. And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ.
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