Musannaf Ibn Abi Shayba 18:896

Abu Bakr narrated to us, he said: Abu Usama narrated to us, from Hisham, from al-Hasan, he said: The one who is killed in the Sacred Precinct (al-Haram) is not to have an increase over the blood money (diyah) of the one who is killed outside the Sacred Precinct.