The blood of the covenant at Sinai
Hebrews quotes Moses' words over the blood of the covenant while explaining that the first covenant was inaugurated with blood.
That is why even the first covenant was not put into effect without blood. For when Moses had proclaimed every commandment of the law to all the people, he took the blood of calves and goats, along with water, scarlet wool, and hyssop, and sprinkled the scroll and all the people, saying, “This is the blood of the covenant, which God has commanded you to keep.”
Exodus 24:8 records Moses sprinkling the people and declaring the blood of the covenant; Hebrews 9:18-20 recounts that inauguration and quotes Moses' declaration.