Exodus 17: 3 - 7
3 But the people thirsted there for water, and the people murmured against Moses, and said, "Why did you bring us up out of Egypt, to kill us and our children and our cattle with thirst?"
4 So Moses cried to the LORD, "What shall I do with this people? They are almost ready to stone me."
5 And the LORD said to Moses, "Pass on before the people, taking with you some of the elders of Israel; and take in your hand the rod with which you struck the Nile, and go.
6 Behold, I will stand before you there on the rock at Horeb; and you shall strike the rock, and water shall come out of it, that the people may drink." And Moses did so, in the sight of the elders of Israel.
7 And he called the name of the place Massah and Mer'ibah, because of the faultfinding of the children of Israel, and because they put the LORD to the proof by saying, "Is the LORD among us or not?"

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