Abdullah bin Abi Bakr (may Allah have mercy on him) narrates from his father (may Allah have mercy on him) that in the letter which the Prophet (peace and blessings be upon him) wrote and gave to Amr bin Hazm (may Allah be pleased with him) there was also: "For a head wound that is deep there is one third of the blood money for a life, and likewise for an abdominal wound."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16206
Amr bin Shu'ayb narrates from his father, and he from his grandfather (Sayyiduna Abdullah bin Amr, may Allah be pleased with them both), that the Prophet (peace and blessings be upon him) ruled: "For a deep head wound, one third of the blood money for a life, 33 and one third camels, or its value in gold, silver, cows or goats; and for an abdominal wound it is the same."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16207