Numbers 10:2-4

2Make thee two trumpets of silver; of a whole piece shalt thou make them: that thou mayest use them for the calling of the assembly, and for the journeying of the camps.

3And when they shall blow with them, all the assembly shall assemble themselves to thee at the door of the tabernacle of the congregation.

4And if they blow but with one trumpet, then the princes, who are heads of the thousands of Israel, shall assemble themselves to thee.