Qedoshim Pereq 4 (CC:III, 1.A, 7.B.; Neusner)

"You shall not hate your brother in your heart, [but reasoning, you shall reason with your neighbor, lest you bear sin because of him. You shall not take vengeance or bear any grudge against the sons of your own people, but you shall love your neighbor as yourself: I am the Lord]" (Lev. 19:17-18).

R. Aqiba says, "This is the encompassing principle of the Torah."