Musannaf Ibn Abi Shayba 18:256

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: 'Amr ibn Muslim informed me that he heard Tawus saying: "The teeth in the upper part of the mouth and the lower part are preferred over the molars." And he said regarding the molars: "The young of the camels."