Musnad Ahmad 132:42

Hassan narrated to us, Ibn Lahi'ah narrated to us, Yazid ibn Abi Habib narrated to us, from Ibn Mu'adh ibn Anas, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not take animals as chairs. For many a ridden animal is more in remembrance of Allah the Exalted than its rider."