וְכִ֨י יִרְדֹּ֜ף גֹּאֵ֤ל הַדָּם֙ אַֽחֲרָ֔יו וְלֹֽא־יַסְגִּ֥רוּ אֶת־הָרֹצֵ֖חַ בְּיָד֑וֹ כִּ֤י בִבְלִי־דַ֙עַת֙ הִכָּ֣ה אֶת־רֵעֵ֔הוּ וְלֹֽא־שֹׂנֵ֥א ה֛וּא ל֖וֹ מִתְּמ֥וֹל שִׁלְשֽׁוֹם׃
And if the avenger of blood pursue after him, then they shall not deliver up the manslayer into his hand; because he smote his neighbour unawares, and hated him not beforetime.
Read midrashic interpretation of Joshua 20:5: and classical rabbinic exegesis.