Musannaf Ibn Abi Shayba 18:197

Abu Bakr narrated to us, he said: Muhammad bin Bakr narrated to us, from Ibn Jurayj, he said: Ibn Abi Najih informed me, from Mujahid, he said regarding the lips: "Fifty [camels] for the two lips, fifty [camels]. And the lower [lip] is preferred over the upper [lip] for both the man and the woman in terms of the severity [of the compensation], but it is not preferred by an increase in the number. Rather, the fifty [for the lower lip] has a severity in the teeth of the camels."