'Innocent Blood' in the Bible

For he did put his life in his hand, and slew the Philistine, and the LORD wrought a great salvation for all Israel: thou sawest it, and didst rejoice: wherefore then wilt thou sin against innocent blood, to slay David without a cause?

Your conscience will not be overwhelmed with guilt for having poured out innocent blood and for having taken matters into your own hands. When the Lord has granted my lord success, please remember your servant."