(6) Yehoshua ben Perachiah and Nittai of Arbel received the transmission [of the oral tradition] from them. Yehoshua ben Perachia said, Make for yourself a teacher (rav), acquire for yourself a companion (chaver); and judge every person as though their intentions are meritorious.
Why ought we judge everyone so positively?
מאי דכתיב (משלי כז, יז) ברזל בברזל יחד לומר לך מה ברזל זה אחד מחדד את חבירו אף שני תלמידי חכמים מחדדין זה את זה בהלכה
Why does the verse teach Iron sharpens iron, as a person sharpens the countenance of his fellow (Proverbs 27:17)? To say to you: “just as this iron [weapon] sharpens the other, so two students of the Wise sharpen one another in the Law”
(יז) כָּל מַחֲלוֹקֶת שֶׁהִיא לְשֵׁם שָׁמַיִם, סוֹפָהּ לְהִתְקַיֵּם. וְשֶׁאֵינָהּ לְשֵׁם שָׁמַיִם, אֵין סוֹפָהּ לְהִתְקַיֵּם. אֵיזוֹ הִיא מַחֲלוֹקֶת שֶׁהִיא לְשֵׁם שָׁמַיִם, זוֹ מַחֲלוֹקֶת הִלֵּל וְשַׁמַּאי. וְשֶׁאֵינָהּ לְשֵׁם שָׁמַיִם, זוֹ מַחֲלוֹקֶת קֹרַח וְכָל עֲדָתוֹ:
(17) Every argument that is [for the sake of] heaven's name, it is destined to endure. But if it is not [for the sake of] heaven's name -- it is not destined to endure. What [is an example of an argument for the sake of] heaven's name? The argument of Hillel and Shammai. What [is an example of an argument not for the sake of] heaven's name? The argument of Korach and all of his followers.