Sayyiduna 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 the killer was brought, dragging his rope. the Messenger of Allah (peace and blessings be upon him) said to the guardian of the slain man: "Will you pardon him?" He said: No. He said: "Then will you take (the blood money)?" He said: No. He said: "Then will you kill him?" He said: Yes. He repeated this to him three times. Then the Messenger of Allah (peace and blessings be upon him) said to him: "If you pardon him, he will bear the burden of his own sin." He said: So he pardoned him. And I saw him dragging his rope, having been pardoned.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18328