Abu Sa’eed (radhi Allahu anhu) narrated that the Messenger of Allah (sallallahu alaihi wa sallam) said:
“The Sirat(the bridge) will be placed across Hell, on thorns like the thorns of Sa’dan plant.* Then the people will cross it. Some will pass over safe and sound, some will be detained, and some will fall in headfirst.”


Sunan Ibn Majah Book 37, Hadith 4421.