This passage explicitly counts and analyzes the Levitical cities, including the forty-two-city total, and is the most direct Chazal source for the arei miklat side of the comparison.
וְתוּ לֵיכָּא? וְהָא כְּתִיב: ״וַעֲלֵיהֶם תִּתְּנוּ אַרְבָּעִים וּשְׁתַּיִם עִיר״! אָמַר אַבָּיֵי: הַלָּלוּ, קוֹלְטוֹת בֵּין לְדַעַת בֵּין שֶׁלֹּא לְדַעַת. הַלָּלוּ – לְדַעַת קוֹלְטוֹת, שֶׁלֹּא לְדַעַת אֵינָן קוֹלְטוֹת.
The Gemara asks: And are there no more cities of refuge beyond these six? But isn’t it written: “And the cities that you shall give to the Levites: The six cities of refuge you shall give for the murderer to flee there, and beyond them you shall give forty-two cities” (Numbers 35:6), indicating that the status of all the Levite cities is that of cities of refuge? Abaye said: With regard to these six cities designated specifically for this purpose, unintentional murderers in need of refuge are admitted there whether they entered the cities deliberately, aware that they are cities of refuge, or whether they entered inadvertently. By contrast, with regard to those forty-two Levite cities, unintentional murderers are admitted only if they entered the cities deliberately, but if they entered the cities inadvertently, they are not admitted to the cities.