Numbers 10:8-10

81The sons of Aaron, moreover, the priests, shall blow the trumpets; and this shall be a permanent statute for you throughout your generations. 9And when you go to war in your land against the enemy who 2attacks you, then you shall sound an alarm with the trumpets, so that you will be 3thought of by the Lord your God, and be saved from your enemies. 10Also on the day of your joy and at your appointed 4feasts, and on the first days of your months, 5you shall blow the trumpets over your burnt offerings, and over the sacrifices of your peace offerings; and they shall be as a reminder of you before your God. I am the Lord your God.”