Al-Imam Ibnul Qayyim, may Allah have mercy upon him, said:

“…Whosever wrongs you and comes and apologizes for his wrongness, then the trait of humbleness obliges upon you to accept his apology whether it be true or false and to leave his hidden affairs to Allah ta’alaa. (This is) as the Messenger, alayhi as-salaatu was-salaam had done with the hypocrites, those who fell behind from joining him in the battle. So when he, alayhi as-salaatu was-salaam, arrived (back) they came to him apologizing to him, whereas he accepted their excuses and left their hidden affairs to Allah Ta’alaa. From the signs of nobility and humbleness is that if you see deficiency in his apology then do not take him to account for it and do not debate with him. Rather, say perhaps the affair is as you say. And if something has been decreed then it will occur and there is no prevention of it…”

Ref: Madaarij as-Saalikeen (333/2)

As al-Imam ash-Shaafi’e, may Allah have mercy upon said:

دية الذنب الاعتذار

The blood-money of a sin is by apologizing