Musannaf Ibn Abi Shayba 33:374

Mu'awiyah ibn Hisham narrated to us, he said: Sufyan narrated to us, from al-A'mash, from 'Amr ibn Murrah—or someone else—from Salim ibn Abi al-Ja'd, he said: Two oxen passed by Abu al-Darda' while they were working. One of them stood up, so the other stood up. Abu al-Darda' said: "Indeed, in this is a lesson."