Alqamah bin Wa'il (may Allah have mercy on him) said that his father (may Allah be pleased with him) told him: We were with the Prophet (peace and blessings be upon him) when a man was brought with a strap tied around his neck. When they reached him (peace and blessings be upon him), he (the claimant) said: This man and my brother were digging a well when he raised a pickaxe, struck my brother on the head with it and killed him. He (peace and blessings be upon him) said: "Pardon him." He refused. He (peace and blessings be upon him) said: "Take the blood money." He said: I do not want the blood money either. Then he (peace and blessings be upon him) again spoke of pardon and blood money, and he refused. So he (peace and blessings be upon him) said: "If you kill him, you will be like him." He said: Then what should I do? He said: "Pardon him." He said: I saw him taking him back by his strap until they disappeared from our sight.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16053