Numbers 10:9-10

When you go into battle in your own land against an enemy who is oppressing you, sound a blast on the trumpets. Then you will be remembered by the LORD your God and rescued from your enemies. Also at your times of rejoicing—your appointed festivals and New Moon feasts—you are to sound the trumpets over your burnt offerings and fellowship offerings, and they will be a memorial for you before your God. I am the LORD your God.”