Num 35:6

וְאֵ֣ת הֶֽעָרִ֗ים אֲשֶׁ֤ר תִּתְּנוּ֙ לַלְוִיִּ֔ם אֵ֚ת שֵׁשׁ־עָרֵ֣י הַמִּקְלָ֔ט אֲשֶׁ֣ר תִּתְּנ֔וּ לָנֻ֥ס שָׁ֖מָּה הָרֹצֵ֑חַ וַעֲלֵיהֶ֣ם תִּתְּנ֔וּ אַרְבָּעִ֥ים וּשְׁתַּ֖יִם עִֽיר׃

Six of the cities you give the Levites are to be appointed as cities of refuge, to which a manslayer may flee. In addition to these, give the Levites forty-two other cities.