Exodus 24:5-8

Then he sent some of the young Israelite men to present burnt offerings and to sacrifice bulls as peace offerings to the LORD. Moses drained half the blood from these animals into basins. The other half he splattered against the altar. Then he took the Book of the Covenant and read it aloud to the people. Again they all responded, “We will do everything the LORD has commanded. We will obey.” Then Moses took the blood from the basins and splattered it over the people, declaring, “Look, this blood confirms the covenant the LORD has made with you in giving you these instructions.”