Numbers 10:8-10

8“The sons of Aaron, the priests, are to blow the trumpets. This is to be a lasting ordinance for you and the generations to come.

9When 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.

10Also 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.”