Al-Zuhri (may Allah have mercy on him) said: The Sunnah has been established that there is no diyah (blood money) upon the 'aqilah (paternal kinsmen) in deliberate killing, except if they wish to pay it of their own goodwill. Yahya (may Allah have mercy on him) said: I have found the people upon this same position.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16363