Musannaf Ibn Abi Shayba 18:672

Abu Bakr narrated to us, he said: Ali bin Mushir narrated to us, from al-Shaybani, from al-Sha’bi, who said: Hisham bin Hubayra, the judge of Basra, wrote to Shurayh asking him about the eye of a beast of burden. He wrote back to him: "In the eye of a beast of burden is a quarter of its price."