One of the reasons to avoid retaliation or taking revenge is facing the justice of Allah on the Day of Qiyamah where each action and every deed of ours would be judged. If our retaliation exceeds the harm or pain that was inflicted upon us, then it will be counted as our misdeed and we would be subjected to punishment.

A point worthy of being noted is that On the Day of Qiyamah, our unjust slapping would not be awarded a punishment of an equal slap. Instead, to make up for our misdeed, our good deeds would be given to the victim. This truly would be a great loss for us.

There is also a possibility that your victim may be awarded with all of your good deeds. Abu Huraira reported Allah's Messenger (ﷺ) as saying:

Do you know who is poor? They (the Companions of the Holy Prophet) said: A poor man amongst us is one who has neither dirham with him nor wealth. He (the Holy Prophet) said: The poor of my Ummah would be the one who would come on the Day of Resurrection with prayers and fasts and Zakat but (he would find himself bankrupt on that day as he would have exhausted his funds of virtues) since he hurled abuses upon others, brought calumny against others and unlawfully consumed the wealth of others and shed the blood of others and beat others, and his virtues would be credited to the account of one (who suffered at his hand). And if his good deeds fall short to clear the account, then his sins would be entered in (his account) and he would be thrown in the Hell-Fire.

Sahih Muslim Book 32: 6251

Thus, many people in this life are doing good deeds but it would be the victims (of their transgression), who would benefit from them. Our good deeds would be given to our victim and the punishment for their sins would be given to us. Even if we have been wronged, it is always better to avoid taking revenge.

 Even a little excess in our retaliation can turn us from a victim into a transgressor (zalim).

But whoever forgives and makes reconciliation, his reward is with Allâh.

Allah encourages to forgive and reconcile and to take reward from Him. In the next verses, Allah makes a huge announcement about forgiveness:

And verily, whosoever shows patience and forgives that would truly be from the things recommended by Allâh.

(Surah Shura- verses-43)

He encourages two things; self control through patience (sabr) and forgiveness. Being patient when facing the hardships or harm caused by people is more difficult than being patient over loss in business etc. Sometimes, we become patient only with the passage of time or when others have cooled us down. At other times, we attain Sabr (patience) as soon as we are hit with a calamity. Glad tidings are to only those who observed Sabr as soon as they were hit with the calamity,as the Prophet ﷺ (peace be upon him) said:

“Sabr is at the first stroke of calamity.”

 There are many verses in the Qur’an where the believers are advised to adopt the Akhlaq of our  Prophet ﷺ. May Allah SWT help us to understand the Akhlaq of our Prophet SAW and implement it in our daily lives. Ameen.