Numbers 10:4

ואם באחת יתקעו AND IF THEY BLOW BUT WITH ONE TRUMPET (i.e. a “Tekiah” on one trumpet) — it is a sign to summon the princes, as it is said here, “then the princes shall gather themselves unto thee”. Their meeting place, too, was at the entrance of the tent of meeting. This is derived from a ג"ש in the Sifrei (Sifrei Bamidbar 73:1 from the use in both cases of the same expression ותקעו and יתקעו: not from ונועדו — ונועדו as erroneously stated.)

וְאִם־בְּאַחַ֖ת יִתְקָ֑עוּ וְנוֹעֲד֤וּ אֵלֶ֙יךָ֙ הַנְּשִׂיאִ֔ים רָאשֵׁ֖י אַלְפֵ֥י יִשְׂרָאֵֽל׃

And if they blow but with one trumpet, then the princes, the heads of the thousands of Yisra᾽el, shall gather themselves to thee.