Exodus 35:2

35:2 Six days shall work be done, but on the seventh day there shall be to you an holy day, a sabbath of rest to the LORD: whosoever doeth work therein shall be put to death.

Numbers 15:32-36

15:32 And while the children of Israel were in the wilderness, they found a man that gathered sticks upon the sabbath day. 15:33 And they that found him gathering sticks brought him unto Moses and Aaron, and unto all the congregation. 15:34 And they put him in ward, because it was not declared what should be done to him. 15:35 And the LORD said unto Moses, The man shall be surely put to death: all the congregation shall stone him with stones without the camp. 15:36 And all the congregation brought him without the camp, and stoned him with stones, and he died; as the LORD commanded Moses.