Leviticus 9:6-7

6Moses said to the people, ‘The Lord has told you that you must do this. Do it. And then the Lord will show you how great he is.’

7Moses said to Aaron, ‘Go to the altar. Sacrifice your sin offering and your burnt offering to the Lord. You must do that to pay for your sins and those of the people. Then sacrifice the people's gift. Their offerings are an atonement for the bad things that they have done. The Lord said that you should do this.’