Musannaf Ibn Abi Shayba 18:1340

Abu Bakr narrated to us, he said: Mu'awiyah ibn Hisham narrated to us, he said: Sufyan narrated to us, from Ma'mar, from a man, from Ikrimah, who said: There is no "aggravated" (mughallazah) [blood money] in dinars and dirhams. The "aggravated" [blood money] is only in camels.