Numbers 10:8-10

8The priests, the sons of Aaron, must use the trumpets to make a noise. This is a rule for you and for all your descendants.

9Use the trumpets to tell everyone when an enemy is attacking you in your own land. Make a sound with the trumpets to tell the people that they must fight the enemy. Then the Lord your God will hear and he will save you from your enemies.

10You must make sounds with the trumpets on your happy days, too. And you must make sounds with the trumpets at your regular festivals and on the first days of your months. And you must make sounds with the trumpets over your burnt offerings, and over your friendship offerings. God will hear and he will remember you. I am the Lord your God.’