Musnad Ahmad 675:4

Khalaf ibn al-Walid narrated to us, Abbad—meaning Ibn Abbad—narrated to us, he said: Khalid al-Hadhdha’ narrated to us, from al-Hakam ibn Utaybah, from Ibn Abi Layla, from Abdullah ibn Ukaym al-Juhani, who said: The letter of the Messenger of Allah (may Allah bless him and grant him peace) came to us in the land of Juhaynah—and I was a young boy, a month or two before his death—saying: "Do not benefit from the dead animal by way of its hide, nor its sinew."