"Rabbi Yohanan ben Zakkai said, Go forth and see which is the good way to which a man should cleave. Rabbi Eliezar said, A good eye; Rabbi Joshua said, A good friend; Rabbi Jose said, A good neighbor; Rabbi Simeon said, One who foresees the fruit of an action; Rabbi Elazar said, A good heart. Thereupon he said to them, I approve the words of Elazar ben Arach, rather than your words, for in his words yours are included."
Mishnah, Abot 2.13
"So, too, in matters affecting a person's relations with his fellow, as soon as there rises from his heart to his mind any animosity or hatred, G-d forbid, or jealousy, anger, or a grudge and the like, he allows them no entrance into his mind and will. On the contrary, his mind exercises its authority and power over the feelings in his heart to do the very opposite, namely, to conduct himself towards his fellow with the quality of kindness and a display of abundant love to the extreme limits, without becoming provoked into anger, G-d forbid, or to revenge in kind, G-d forbid, but rather to repay the offenders with favors, as taught in the Zohar, that one should learn from the example of Yosef [Joseph] towards his brothers."
Tanya ch 12
"The world stands upon three things: upon the Law, upon worship, and upon showing kindness."