Assalaamu alaykum. My question is regarding forgiving others who have hurt you: is it enough to forgive the person by saying, 'I forgive you,' while the feelings of hatred are still present in the heart? I have tried forgiving a person who backbit about me; I said, "I forgive him," but not in his presence. I even backbit about him, so if I forgive him and he does not forgive me, will I be the one suffering in hereafter?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

Pardoning the one who wrongs you means that the wronged person gives up his right to retaliation for the transgression on his rights, clearing the transgressor of their liability. Ibn Qudaamah wrote, "Chapter on the virtues of pardon and kindness: pardon means giving up a right to which he is entitled..." [Mukhtasar Minhaaj Al-Qaasideen]

When the wronged person gives up his right, he has pardoned the one who has wronged him. The fact that the heart of the wronged person still harbors hatred and resentment towards the one who wronged him is irrelevant, especially given that one has no control over the matters of the heart. For more benefit, please refer to fatwas 84351 and 89899.

If you have wronged any person, like in the case mentioned in the question, which is backbiting, then that is a totally different situation which is independent from his transgression against you. If he does not forgive you, then you are still liable for this transgression. However, if you repent to Allah, The Exalted, of the sin of backbiting, praise that person in the gatherings in which you backbit him, supplicate Allah in his favor, and implore Him to forgive him, then you shall not be held accountable for it, hopefully. For more benefit, please refer to fatwa 82148.

Allah knows best.