Exodus 32:28

"So the sons of Levi did as Moses instructed, and about three thousand men of the people fell that day".

"As Moses came down the mountain with the two tablets of stone, he saw that the people below were worshipping a golden calf. On that day the law arrived and at Moses command 3, 000 people were executed for their sin. When grace arrived on the Day of Pentecost, Peter came down from the Upper Room to announce the New Covenant. He didn't say "We're scrapping OT laws and bringing in some NT laws".
No he came down with grace and the people below were not worshipping a golden calf. They had done something far worse. They had crucified the Lord of glory. But on that day the Bible says that 3, 000 were saved!".

Ref: Ref: Rob Rufus - "Living in the Grace of God" - Authentic Media (2007) - (p28-29).