מדרש אויף במדבר 10:6

(Numb. 31:1, 2, 6:) THEN THE LORD SPOKE UNTO MOSES, SAYING: EXACT VENGEANCE FOR THE CHILDREN OF ISRAEL <ON THE MIDIANITES>. […. WITH THE VESSELS OF THE SANCTUARY AND THE TRUMPETS FOR SOUNDING THE ALARM IN HIS HAND.] Let our master instruct us: How many sustained blasts (teqi'ot) does one blow on eve of the Sabbath to detach the people from labor?⁷Tanh.,Numb. 9:2. Thus have our masters taught (in Suk. 5:5): ONE BLOWS THREE SUSTAINED BLASTS TO HAVE THE PEOPLE CEASE FROM LABOR.⁸See Shab. 35b. How? The hazzan of the congregation takes the trumpets and goes up to the roof at the highest point in the city and blows. <Thereupon> whoever is far from the city leaves his work. Then he comes again and blows a second time. <Thereupon> those who are nearer enter the city. When he blows a third time, they place the hammin⁹I.e., the Sabbath food kept warm from Friday. in the oven and light the <Sabbath> lights. <If> he has finished blowing <while> the pot was on the stove, they set it on the ground. If there was a light in a woman's hand, she set it on the ground. The Sabbath is sanctified with trumpets, and so also are New Moons and Festivals, as stated (in Numb. 10:10): WHEN YOU HAVE A DAY OF REJOICING, AT YOUR FIXED FESTIVALS, AND ON YOUR NEW MOONS, YOU SHALL BLOW THE TRUMPETS. Moreover, when they moved out <from camp>, they blew the trumpets to move out, as stated (in Numb. 10:6): WHEN YOU BLOW a [SECOND] SHORT BLAST (teru'ah), THE CAMPS <PLACED TO THE SOUTH> SHALL MOVE OUT…. Also when <the congregation> met together, they blew the trumpets, as stated (in vs. 7): WHEN THE CONGREGATION ASSEMBLES, YOU SHALL BLOW <SUSTAINED BLASTS AND NOT SHORT ONES>. And when an enemy oppresses you, you shall blow the trumpets, as stated (in vs. 9): AND WHEN YOU GO TO WAR IN YOUR LAND AGAINST AN ENEMY WHO OPPRESSES YOU, YOU SHALL BLOW THE TRUMPETS. And when they went to take vengeance against Midian, they carried out their vengeance with trumpets, as stated (in Numb. 31:6): WITH THE VESSELS OF THE SANCTUARY AND THE TRUMPETS FOR SOUNDING THE ALARM (teru'ah) IN HIS HAND.