Mishnah 12 - Chapter 1 - Pirkei Avot

Hillel and Shammai received it from them. Hillel says: Be of the disciples of Aaron, loving peace and pursuing peace, loving men and drawing them close to Torah. [They explained in Avoth d' R. Nathan how Aaron loved peace. When he saw two men quarreling, he would go to each one without the knowledge of the other and say to him: "Look at your friend. See how he regrets what he has done and how he smites himself for having sinned against you. He asked me to come to you and beg you to forgive him." Afterwards, when they met, they would kiss each other. And how would he draw men close to Torah? When he knew a man to have transgressed, he would befriend him and look kindly upon him — whereupon the other would think, in shame: "If that tzaddik knew of my evil deeds, how he would distance himself from me!" As a result, he would repent. This is the testimony of the prophet (Malachi 2:6): "In peace and justness did he (Aaron) walk with Me, and many did he turn from sin."]