What did God say would come out of the rock when Moses smote it?
God promised that when Moses struck the rock, water would flow out of it. That water was to supply not only all those millions of people but also all their livestock, showing God's provision for the entire camp in the wilderness.
Les explains that God told Moses to smite the rock, and out of it would come water. This was not a small amount; it was enough for all those millions of people and for all their livestock. The passage goes on to note that a river of water came out of that rock, and later Amalek came and tried to make war over that water.
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.