Praise be to Allah.

Firstly:

The siraat is a bridge that will be set up over the top of Hell, as is explained clearly in the saheeh hadiths. The disbelievers will not pass over it; rather the believers will pass over it in ways that will vary according to their merits.

As for the disbelievers and polytheists, they will enter Hell in groups, before the siraat is set up.

This is indicated by the report narrated by al-Bukhaari (6573) and Muslim (182) from Abu Hurayrah, who said: Some people said to the Messenger of Allah (blessings and peace of Allah be upon him): O Messenger of Allah, will we see our Lord on the Day of Resurrection? The Messenger of Allah (blessings and peace of Allah be upon him) said: “Do you have any trouble seeing the sun when there are no clouds in front of it?” They said: No, O Messenger of Allah. He said: “Do you have any trouble seeing the moon on the night when it is full and there are no clouds in front of it?” They said: No, O Messenger of Allah. He said: “Similarly you will see Him on the Day of Resurrection. Allah will gather all the people and will say: ‘Whoever used to worship anything, let him follow it.’ So those who used to worship the sun [will follow the sun], those who used to worship the moon [will follow the moon], and those who used to worship false gods [will follow the false gods]. There will remain this ummah, including its hypocrites.  Then Allah [may He be blessed and exalted] will come in a form other than the form which they know, and He will say, ‘I am your Lord.’ They will say: ‘We seek refuge in Allah from you. We will stay here until our Lord comes, and when our Lord comes, we will recognize Him.’ Then Allah will come to them in the form which they know, and will say, ‘I am your Lord.’ They will say, ‘You are our Lord,’ and they will follow Him. Then a bridge will be set up over Hell.” The Messenger of Allah (blessings and peace of Allah be upon him) said: “And I and my ummah will be the first ones to cross it, and the prayer of the Messengers on that Day will be: ‘O Allah, grant safety, grant safety!’ On it there will be hooks like the thorns of as-sa‘daan (a thorny tree); have you seen the thorns of as-sa‘daan?” They said: Yes, O Messenger of Allah. He said: “They are like the thorns of as-sa‘daan, except that no one knows how big they are except Allah. They will snatch the people according to their deeds. Some of them will be doomed because of their deeds, and some will be cut [by those thorns] then they will be saved.”

Al-Bukhaari (7439) and Muslim (183) narrated that Abu Sa‘eed al-Khudri said: We said: O Messenger of Allah, will we see our Lord on the Day of Resurrection? The Messenger of Allah (blessings and peace of Allah be upon him) said: “Do you have any trouble seeing the sun or the moon when there are no clouds?” We said: No. He said: “Then surely you will not have any trouble seeing your Lord, may He be blessed and exalted, on that Day, just as you have no trouble seeing either of them.” Then he said: “A caller will announce: ‘Let every people follow that which they used to worship,’ then those who worshipped the cross will go with their cross, and those who worshipped idols will go with their idols, and those who worshipped any [false] gods will go with their gods, until there will be left those who used to worship Allah, righteous and evildoers alike, and the remnants of the people of the Book. Then Hell will be brought, and will be shown as if it is a mirage. It will be said to the Jews:  ‘What did you worship?’ They will say: ‘We used to worship ‘Uzayr the son of God.’ It will be said to them: ‘You are lying, for Allah has neither wife nor son. What do you want?’ They will say: ‘We want You to give us to drink.’ It will be said: ‘Drink,’ and they will fall into Hell. Then it will be said to the Christians: ‘What did you worship?’ They will say: ‘We used to worship the Messiah, the son of God.’ It will be said to them: ‘You are lying, for Allah has neither wife nor son. What do you want?’ They will say: ‘We want You to give us to drink.’ It will be said: ‘Drink,’ and they will fall into Hell. And then there will be no one left except those who worshipped Allah, righteous and evildoers alike. It will be said to them: ‘What are you waiting for? All the people have gone.’ They will say: ‘We kept ourselves away from them and now we are the most in need of Him, for we heard a caller calling out, Let every people follow that which they used to worship. We are waiting for our Lord.” Then al-Jabbaar [the Compeller] will come to them in a form other than the form in which they saw Him on the first occasion, and will say: ‘I am your Lord.’ They will say: ‘You are our Lord.’ No one will speak to Him except the Prophets, and He will say: ‘Is there any sign between Him and you by which you will recognize Him?’ They will say, ‘The Shin.’ So He will lay bare His Shin, and every believer will prostrate to Him, whereas everyone who used to prostrate to Allah by way of showing off will try to prostrate, but his back will become solid. Then the bridge will be brought and set up over Hell.” We said: O Messenger of Allah, what is the bridge? He said: “A slippery place, in which there are hooks and spikes and thorns, like those in Najd that are called as-sa‘daan. The believer will cross like the blink of an eye, like lightning, like the wind, like the swiftest horses and camels. Some will cross safe and sound, some will be scratched then let go, and some will be piled up in the Fire of Hell, until the last of them crosses it by crawling…”

This clearly indicates that the siraat will only be brought after the disbelievers and polytheists have gone to the Fire.

Based on that, there is no confusion about the verse in Soorat az-Zumar which says that the disbelievers will enter Hell in groups.

Al-Haafiz Ibn Rajab (may Allah have mercy on him) said: You should know that people are divided into two categories: believers who worship Allah alone and do not associate anything with Him, and polytheists who worship others alongside Allah. As for the polytheists, they will not pass over the siraat; rather they will fall into Hell before the siraat is set up. This is indicated by the reports in as-Saheehayn.

Then he quoted part of the hadith of Abu Hurayrah and the hadith of Abu Sa‘eed, then he said:

This hadith clearly indicates that everyone who worshipped anything other than Allah – such as the Messiah and ‘Uzayr among the People of the Book – will be joined with the polytheists in falling into Hell before the siraat is set up.

End quote from at-Takhweef min an-Naar (p. 236).

Dr. ‘Umar Sulaymaan al-Ashqar (may Allah have mercy on him) said: Those who will pass over the siraat are the believers, not the polytheists. The hadiths that we have quoted indicate that the disbelieving nations will follow the false gods that they used to worship; those false gods will be followed by their worshippers until they fall with them into Hell. After that will be left the believers, with the hypocrites and sinful believers among them; these are the ones for whom the siraat will be set up.

End quote from al-Qiyaamah al-Kubra (p. 275).

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: No one will cross the siraat except the believers, in a manner commensurate with their deeds, because of the hadith of Abu Sa‘eed (may Allah be pleased with him), from the Prophet (saw), in which it says that the believers will cross like the blink of an eye, like lightning, like the wind, like birds, like the swiftest horses and camels; some will cross safe and sound, some will be scratched and let go, and some will be piled up in Hell. (Agreed upon).

In Saheeh Muslim it says that their deeds will make them run, and your Prophet will be standing on the siraat, saying: O Lord, grant safety, grant safety, until people’s deeds are no longer able to make them walk, then a man will come, unable to walk and only able to crawl. In Saheeh al-Bukhaari, it says: … until the last of them will be dragged.

End quote from Majmoo‘ al-Fataawa (5/69).

Secondly:

It is said that the Zoroastrians believe in the siraat, which [according to their beliefs] is a bridge that separates the world of the living and the world of the dead; all people will pass over this bridge at the time of death. If a person was evil, the bridge will become narrow and the devil will come out to drag his soul to the place of eternal punishment, and if he was good, the bridge will become wide enough for this person to cross it safely.

This concept – as is quite obvious – does not refer to the siraat that is mentioned in the saheeh hadiths narrated from the Prophet (blessings and peace of Allah be upon him).

For more information about the Zoroastrians and some of their beliefs, please see: https://goo.gl/if96Pq

It does not concern us that the beliefs of earlier religions may include things that are similar to what the Muslims believe. What is most likely to be the case is that this is something that they learned from their Prophets and it remained among them even after they began to associate others with Allah and went astray, as many rituals and beliefs remained with the polytheist Arabs that they had learned from Ismaa‘eel (peace be upon him) or that they had heard from the Jews who lived among them. Allah, may He be exalted, says (interpretation of the meaning): “and there was no nation but that there had passed within it a warner” [Faatir 35:24].

With regard to the view that Islam took this idea from them, that is so obviously flawed that there is no need for evidence. The Prophet (blessings and peace of Allah be upon him) did not know anything about the beliefs of the Zoroastrians, or even the knowledge of the people of the Book who came before him, and he did not speak from [his own] inclination; rather it was but a revelation revealed.

Allah, may He be exalted, says (interpretation of the meaning):

“And you did not recite before it any scripture, nor did you inscribe one with your right hand. Otherwise the falsifiers would have had [cause for] doubt.

Rather, the Qur'an is distinct verses [preserved] within the breasts of those who have been given knowledge. And none reject Our verses except the wrongdoers”

[al-‘Ankaboot 28:48-49].

There is proof and evidence of the soundness of Islam, the miraculous nature of the Qur’an and that it is the word of Allah, and the soundness of the prophethood of our Prophet (blessings and peace of Allah be upon him), which leaves no room for doubt for anyone who has common sense and has any knowledge of that. Moreover, how could a Muslim think that this is possible? We should point out that researching other religions and studying specious arguments is not appropriate except for one who is well-versed in sound Islamic knowledge and has a good understanding of the Qur’an and Sunnah. If you are unaware of what is narrated in as-Saheehayn about the siraat, then how can you justify looking at the scriptures of the Zoroastrians?

Our advice to you is to seek sound knowledge first, and do not expose yourself to that which could lead to doom, for if one who has little knowledge indulges in a lot of discussion and research, it will be very bad for him.

One of the salaf [early generations] indeed spoke the truth when he said: Hearts are weak, and a specious argument could snatch one away (from the straight path).

We ask Allah to help and guide you.

And Allah knows best.