Musannaf Ibn Abi Shayba 18:374

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ash'ath, from 'Amir, from 'Ali and 'Abdullah, they both said regarding the glans (of the penis): "If it is cut off, the full blood money (diyah) is due, and whatever is missing from it, then it is by calculation."