וַיִּמָּֽסְרוּ֙ מֵאַלְפֵ֣י יִשְׂרָאֵ֔ל אֶ֖לֶף לַמַּטֶּ֑ה שְׁנֵים־עָשָׂ֥ר אֶ֖לֶף חֲלוּצֵ֥י צָבָֽא׃
So there were delivered, out of the thousands of Israel, a thousand of every tribe, twelve thousand armed for war.
Read Kabbalistic (mystical) interpretations of Numbers 31:5: Zohar and classical Jewish mystical sources, free online.