הלכה אויף עמוס 1:11

It is forbidden for man to be ill-natured and unforgiving, for he must be easily appeased but unwidely to wrath; and when a sinner implores him for pardon, he should grant him pardon wholeheartedly and soulfully. Even if one persecuted him and sinned against him exceedingly he should not be vengeful and grudge-bearing, for such is the path of the seed of Israel and of their excellent heart. Only the idolaters are not so, they are of uncircumcised heart, and their wrath is ever-watchful; and, because the Gibonites were unforgiving and unappeasing, that of them it is said: "Now the Gibonites were not of the children of Israel" (II. Samuel, 21.2).¹¹Baba Kamma, 92a. C.

Sins committed against your fellow man are not atoned for on Yom Kippur unless you placate him, as it is said, "You will be cleansed of all your sins before God." This means, only sins against God are atoned for on Yom Kippur, but sins committed against your neighbor are not atoned for on Yom Kippur, unless you placate your neighbor. Everyone must, therefore, be very careful, if he has in his possession illegally acquired property, to return it and placate [the rightful owner]. If you are holding property of which you are not certain whether or not it legally belongs to you, you should let your neighbor know that you wish to appear with him, immediately after Yom Kippur, before a Beis Din Rabbinical court to be judged according to the holy Torah; and you should firmly resolve to abide by the verdict pronounced by the Beis Din. If you sinned against your neighbor, even if only with words, you must appease him. It is your duty to go personally to appease him. However, if it is difficult for you to do so, or if you understand that he will be reconciled more easily through an intermediary, you should appease him through an intermediary. The person whose forgiveness is asked should forgive wholeheartedly and should not be ruthless, for this is not a Jewish characteristic, but a trait of Esau of whom it is said, "And he kept his anger forever" (Amos 1:11). It is also said of the Gibeonites, because they did not forgive and would not be appeased, "The Gibeonites were not of the Children of Israel." (II Samuel 21:2) The characteristic of the Children of Israel is to be slow to anger and easy to be appeased. And when the sinner asks for forgiveness you should grant forgiveness wholeheartedly and willingly. Even if he tormented you a great deal you should not take revenge nor bear a grudge. On the contrary, if the offender does not take the initiative to come to you asking for forgiveness, you should present yourself to the offender in order that [the offender] should ask your forgiveness. If a person does not banish hatred [from his heart] on Yom Kippur, his prayers will not be heard, God forbid; but if you are tolerant and forgiving, all your sins will be forgiven.