Numbers 10:8-10

8The sons of Aaron, the kohanim will blow the trumpets. This is to be an eternal ordinance for you as well as for your generations to come.

9Whenever you go to war in your own land against the enemy who is hostile to you, you are to sound short blasts of alarm. Then you will be remembered before Adonai your God and be delivered from your enemies.

10Also at your days of rejoicing, feasts and new moons, you are to blow on the trumpets over your burnt offerings and fellowship offerings. They will then be a reminder for you before Adonai your God. I am Adonai your God!”