Perhaps the most memorable example of forgiveness in the novel--and certainly the most surprising to Amir--comes when Baba confronts Hassan about the money and gifts found under his bed, items that Amir has planted himself.
... Baba stunned me by saying, "I forgive you."
Forgive? But theft was the one unforgivable sin, the common denominator of all sins. (Chapter 9)
Baba's love of Hassan is at the root of his generosity, but it is only later in the novel that the reader discovers the true reason for his magnanimous gesture: Hassan is actually Baba's son. Hassan himself has the chance to forgive his own mother for deserting him as a child when Sanaubar suddenly returns to Baba's old home. At first Hassan wants nothing to do with her, but he soon relents.
Hassan dropped her hand and bolted out of the house...
He came back the next morning... (and) took Sanaubar's hand in both of his... she was home now... (Chapter 16)
Amir is finally able to forgive himself for his past indiscretions against Hassan after he returns to Afghanistan to find Sohrab. While he is taking the brutal beating from Assef, Amir realizes that the punishment has cured him of his guilt--it is his atonement.
My body was broken--just how badly I wouldn't know until later--but I felt healed. Healed at last. (Chapter 22)
Hassan forgave Amir for all he did to him, including framing him for theft. Amir was unable to live with the guilt of failing to help Hassan when he was attacked by Assef. Amir accused Hassan of stealing from him, and when Baba confronted him and found the items, Hassan did not deny anything, although he knew what had happened. Ali decided he and Hassan should move out of Baba’s house. Hassan moved on from the event, even asking after Amir from Rahim whenever they met.
General Taheri and his wife forgave their daughter and accepted her back in their home after she ran away with an Afghan man. The General searched for his daughter, and when he found her, he took her back home.
Despite Sanaubar abandoning Hassan when he was just a baby, Hassan found it in his heart to forgive her when she came back home after many years.
I would look out the window into the yard and watch Hassan and his mother kneeling together, picking tomatoes or trimming a rosebush, talking. They were catching up on all the lost years, I suppose.