1 Samuel 14:33

Then they told Saul, saying, Behold, the people sin against the Lord, in that they eat with the blood. And he said, Ye have transgressed: roll a great stone unto me this day.

Cross-reference

Leviticus 7:26 forbids eating blood entirely — this is the law Saul says the people have transgressed.

Leviticus 17:10 warns of being cut off for eating blood — adding the consequence of the sin Saul confronts.