Abu Dawud Book 34, Hadith Number 4489.

Chapter : If the legal heir of a man who has been killed intentionally agrees to accept bloodwit the slayer will be asked to pay him.

Narated By AbuShurayb al-Ka’bi : The Prophet (PBUH) said: Then you, Khuza’ah, have killed this man of Hudhayl, but I will pay his blood-wit. After these words of mine if a man of anyone is killed, his people will have a choice to accept blood-wit or to kill him.