Musnad Ahmad 31:213

Rawh narrated to us, Uthman ibn Ghiyath narrated to us, Abu Nadra narrated to us, from Abu Sa’id al-Khudri, from the Prophet, may Allah bless him and grant him peace, that he said: "People will pass over the bridge of Hell." He mentioned it and said: "On its two sides are angels saying: 'O Allah, grant safety, grant safety.'" And he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Have you not seen the *sabgha*? A tree that grows in the flood debris." And he said: "As for the people of the Fire who are its people," and he mentioned the meaning of it.