Musnad Abu Ya'la al-Mawsili 249:1

Sa'id ibn Abi al-Rabi' al-Samman narrated to us, 'Anbasah narrated to us, Hammad, the freed slave of Umayyah, narrated to us, from Janah, the freed slave of al-Walid, from Wathilah ibn al-Asqa', that the Messenger of Allah (may Allah bless him and grant him peace) said: "The best of your youth are those who resemble your elders, and the worst of your elders are those who resemble your youth."