Exodus 32:4-8, 35

And he received the gold from their hand, and he fashioned it with an engraving tool, and made a molded calf. Then they said, “This is your god, O Israel, that brought you out of the land of Egypt!” So when Aaron saw it, he built an altar before it. And Aaron made a proclamation and said, “Tomorrow is a feast to the LORD.” Then they rose early on the next day, offered burnt offerings, and brought peace offerings; and the people sat down to eat and drink, and rose up to play. And the LORD said to Moses, “Go, get down! For your people whom you brought out of the land of Egypt have corrupted themselves. They have turned aside quickly out of the way which I commanded them. They have made themselves a molded calf, and worshiped it and sacrificed to it, and said, ‘This is your god, O Israel, that brought you out of the land of Egypt!’ ”

So the LORD plagued the people because of what they did with the calf which Aaron made.