What is the ruling on forgiving disbelievers who wrong us (such as backbiting or damaging property)? And does the saying of Imam Ahmad, "I forgive anyone except an innovator," apply to them?

Islam encourages tolerance, forgiveness, pardoning, and absolution. It is a religion of mercy, and a Muslim is a bearer of glad tidings, not an alienator, who forgives when able. A Muslim forgives personal harm inflicted upon him by a disbeliever, but this forgiveness should not lead to the Muslim's humiliation, for a Muslim is honorable. Forgiveness is not always praiseworthy; it may be blameworthy if it results in the humiliation of a Muslim or emboldens the aggressor. Forgiveness is praiseworthy if it is for the purpose of reconciliation. It is permissible for a Muslim to waive his right if seeking victory would lead to a greater corruption, as is the case for Muslims living in non-Islamic countries if resisting injustice would provoke greater resentment from the disbelievers. However, if a Muslim can repel injustice and demonstrate the honor of Islam without greater harm, then it is obligatory upon him to do so.