Sayyiduna Abu Umamah (may Allah be pleased with him) narrated: the Prophet (peace and blessings be upon him) said: "Whoever forgives despite having the power (to take revenge), Allah Almighty will pardon him on the Day of Hardship."
Al-Tabarani recorded it; its chain contains a narrator, al-Ala' bin Kathir, who is da'if (weak).