Musannaf Ibn Abi Shayba 18:196

Abu Bakr narrated to us, he said: Muhammad bin Bakr narrated to us, from Ibn Jurayj, he said: I said to 'Ata', "The two lips, what is in them?" He said, "Fifty, fifty [camels] for each one of them." I said, "Is there a difference between them?" He said, "The lower one is preferred, so they claim." I said, "By how much?" He said, "I do not know."