1 Samuel 14:34

And Saul said, Disperse yourselves among the people, and say unto them, Bring me hither every man his ox, and every man his sheep, and slay them here, and eat; and sin not against the Lord in eating with the blood. And all the people brought every man his ox with him that night, and slew them there.

Cross-reference

Genesis 9:4 establishes the Noahic prohibition on eating blood — the foundation for Saul's instruction to slaughter properly.

Leviticus 7:26 reiterates the blood prohibition — Saul's command to slay properly is to avoid this sin.