A--- There are many Hadiths regarding this. Foremost among which are:

Allah's Messenger (Peace be upon him) said in a lengthy Hadith, "Then a bridge will be laid across Hell (Fire). I and my followers will be the first ones to go across it and none will speak on that Day except the Messengers. And the invocation of the Messengers on that Day will be, 'O Allah, save! Save!' In Hell (or over the Bridge) there will be hooks like the thorns of As-Sa' dan (thorny plant).Have you seen As-Sa 'dan?" They replied, "Yes, O Allah's Messenger!" He said: "So those hooks look like the thorns of As-Sa' dan, but none knows how big they are except Allah.

Those hooks will snap the people away according to their deeds. Some of the people will stay in Hell (be destroyed) because of their (evil) deeds, and some will be cut or torn by the hooks (and fall into Hell) and some and then relieved. When Allah has finished His Judgments among the people, He will take whomever He will out of Hell through His Mercy. He will then order the angels to take out of the Fire all those who used to worship none but Allah from among those whom Allah wanted to be merciful to and those who testified (in the world) that none has the right to be worshipped but Allah. The angels will recognize them in the Fire by the marks of prostration (on their foreheads), for the Fire will eat up all the human body except the mark caused by prostration as Allah has forbidden the Fire to eat the mark of prostration. They will come out of the (Hell) Fire, completely burnt and then the water of life will be poured over them and they will grow under it as does a seed that comes in the mud of the torrent." (Bukhari and Muslim)

Abu Sa' id AI-Khudri (May Allah be pleased with him) said: I have come to know that the Bridge (the Straight Path) is thinner than a hair and sharper than the sword.