Musannaf Ibn Abi Shayba 18:88

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Muhammad ibn Ishaq, from Makhul, he said: The Messenger of Allah (may Allah bless him and grant him peace) decreed regarding the *munqilah* (a head wound that fractures the bone and displaces it) fifteen [camels].