Short answer
The Sirat is a bridge set over Hell on the Day of Judgement, which every person must cross to reach Jannah. The hadith describe it as slippery, with hooks and thorns along it. Believers cross at speeds that match their deeds, some like the blink of an eye, while others are caught and fall into the Fire.
Belief in the Sirat is part of Sunni creed, affirmed in al-Tahawiyya and al-Nasafiyya. Ahl al-Sunnah take it as a real bridge, as the sahih hadith describe it, while some Mu'tazilis explained it away.
The four schools agree on this.
Explanation
Allah says: "there is none of you except he will come to it. This is upon your Lord an inevitability decreed" (19:71). Many commentators explained this as everyone passing over the Fire on the Sirat. The Prophet ﷺ said the Sirat will be laid across Hell, and he and his ummah will be the first to cross it, and on that day the messengers will be saying: O Allah, keep safe, keep safe.
The Companions asked what the bridge is like. He said: "A slippery place where feet slip, with hooks and grabbing irons and a wide thorn." Then he described the believers crossing: some like the blink of an eye, some like lightning, some like the wind, some like fast horses and riders. Some are saved unharmed, some are scratched and let go, and some are pushed into the Fire. A Companion's report in Sahih Muslim adds that it is finer than a hair and sharper than a sword.
What carries a person across is faith and deeds. The Quran describes believers on that Day with "their light proceeding before them and on their right" (57:12). Sunni creed also holds that some sinful believers may fall and be punished for a time, then be brought out by intercession and Allah's mercy.
Note that this is a different word use from al-sirat al-mustaqim, the straight path we ask for in al-Fatiha. Read more in barzakh and the afterlife, will the Prophet intercede for us? and what is Hell like?
The evidence
Quran, Surah Maryam 19:71
وَإِن مِّنكُمْ إِلَّا وَارِدُهَا ۚ كَانَ عَلَىٰ رَبِّكَ حَتْمًۭا مَّقْضِيًّۭا ﴿٧١﴾
And there is none of you except he will come to it. This is upon your Lord an inevitability decreed.
Understood by many commentators as everyone crossing over Hell.
Quran, Surah Al-Hadid 57:12
يَوْمَ تَرَى ٱلْمُؤْمِنِينَ وَٱلْمُؤْمِنَٰتِ يَسْعَىٰ نُورُهُم بَيْنَ أَيْدِيهِمْ وَبِأَيْمَٰنِهِم بُشْرَىٰكُمُ ٱلْيَوْمَ جَنَّٰتٌۭ تَجْرِى مِن تَحْتِهَا ٱلْأَنْهَٰرُ خَٰلِدِينَ فِيهَا ۚ ذَٰلِكَ هُوَ ٱلْفَوْزُ ٱلْعَظِيمُ ﴿١٢﴾
On the Day you see the believing men and believing women, their light proceeding before them and on their right, [it will be said], "Your good tidings today are [of] gardens beneath which rivers flow, wherein you will abide eternally." That is what is the great attainment.
Describes the light of the believers on that Day.
Sahih al-Bukhari 7437
Sahih... وَيُضْرَبُ الصِّرَاطُ بَيْنَ ظَهْرَىْ جَهَنَّمَ، فَأَكُونُ أَنَا وَأُمَّتِي أَوَّلَ مَنْ يُجِيزُهَا ...
"The Sirat will be laid across Hell, and I and my ummah will be the first to cross it."
Affirms the bridge over Hell.
Sahih al-Bukhari 7439
Sahih... مَدْحَضَةٌ مَزِلَّةٌ، عَلَيْهِ خَطَاطِيفُ وَكَلاَلِيبُ وَحَسَكَةٌ ...
"A slippery place where feet slip, with hooks, grabbing irons and a wide thorn on it."
Describes the bridge.
Where the ruling is recorded
- al-Aqida al-Tahawiyya, Section on the events of the Day of Resurrection. Lists the Sirat and the Mizan among the things a Muslim believes in.
- al-Aqa'id al-Nasafiyya with Sharh al-Taftazani, Section on the events of the Hereafter. States that the Sirat is true, alongside the Mizan and the reading of the book of deeds.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.