I've come across a very intresting hadith from Sahih al-Bukhari.
Volume 9, Book 93, Number 532s
Some of the believers will cross the bridge as quickly as the wink of an eye, some others as quick as lightning, a strong wind, fast horses or she-camels. So some will be safe without any harm; some will be safe after receiving some scratches, and some will fall down into Hell (Fire). The last person will cross by being dragged (over the bridge)."
The hadith describes the state of different groups of people who will cross the bridge Sirat. The last sentence especially emphasizes the last person to be dragged over the Sirat.
Who is that last person and why is that person mentioned without a further description?