Reference for Isaiah סו:21

וְגַם־מֵהֶ֥ם אֶקַּ֛ח לַכֹּהֲנִ֥ים לַלְוִיִּ֖ם אָמַ֥ר יְהוָֽה׃

And of them also will I take for the priests and for the Levites, saith the LORD.

ספר השרשים