Musnad Abu Ya'la al-Mawsili 159:115

Abu Ubaydah ibn Fudayl ibn Iyad informed us, Mu'ammal ibn Isma'il narrated to us, Hammad ibn Zayd narrated to us, from Ma'mar, from al-Zuhri, from 'Ata' ibn Yazid al-Laythi, from Abu Sa'id and Abu Hurayrah, who both said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Upon the Sirat (bridge) are the thorns of the Sa'dan. Have you seen the Sa'dan?"