Musnad Ahmad 30:1243

Abu Asim narrated to us, Hassan bin Yazid bin Farrukh al-Damri narrated to us, from the people of Medina, he said: I heard Abu Salamah saying: I heard Abu Hurairah saying: I bear witness that I heard the Prophet, peace and blessings of Allah be upon him, saying: "There is no male servant or female servant who swears a sinful oath at this pulpit, even if it were for a moist tooth-stick (miswak), but that the Fire becomes mandatory for him."