Musnad Ahmad 1301:27

Abu Mu'awiyah narrated to us, he said: Ubaydullah ibn al-Walid al-Wassafi narrated to us, from Abdullah ibn Ubayd ibn Umayr, from Abu al-Darda', he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever hears a hadith (speech/account) from a man, and he does not desire that it be mentioned from him, then it is a trust, even if he did not ask him to keep it secret."