Alqamah bin Wa'il (may Allah have mercy on him) relates that his father (Wa'il bin Hujr, may Allah be pleased with him) said: I was present with the Messenger of Allah (peace and blessings be upon him) when a man was brought bound in a rope. The Messenger of Allah (peace and blessings be upon him) said to the guardian of the slain man: "Do you forgive him?" He said: No. He (peace and blessings be upon him) said: "Then will you take the blood money (diyah)?" He said: No. He (peace and blessings be upon him) said: "Then will you kill him?" He said: Yes. He (peace and blessings be upon him) said: "Then take him away." He turned away from him (peace and blessings be upon him), and he (peace and blessings be upon him) said (again): "Come, do you forgive?" as before. The guardian of the slain man refused in the same way three times, and at the fourth time the Messenger of Allah (peace and blessings be upon him) said: "Know that if you forgive him, he will return bearing your sin and the sin of your companion (the slain man)." So he let him go. He said: I saw him dragging his rope.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18226