First:
الصراط or السراط: means path in Arabic only people of al-Hijaz used the Version with "sad ص" and in the quranic readings you may find these two versions and also az-zirat (الزراط).
What i could find in Sunni Books for example in at-tahrir wa at-tanwir التحرير والتنوير from the great scholar Taher ben Ashur is a narration of ibn Abas (may Allah be pleased with both of them) saying it is the true faith/religion دين الحق and in another Versions it is the Islamic faith ملة الإسلام as you find it Surat al An'aam (6:161) discribed
O Muhammad, say, "As for me, my Lord has most certainly guided me on
the Straight Way, the ever True Faith, Abraham's Way which he had
adopted exclusively and whole-heartedly and he was not of mushrikin."
قُلْ إِنَّنِي هَدَانِي رَبِّي إِلَى صِرَاطٍ مُّسْتَقِيمٍ دِيناً
قِيَماً مِّلَّةَ إِبْرَاهِيمَ حَنِيفاً وَمَا كَانَ مِنَ الْمُشْرِكِينَ
Ibn Kathir quoted it and added some other tafsirs for example he said it is the Quran according to a Hadith which has some weakness because of the narrator Al-Harith himself!
Narrated Al-Harith Al-A'war: "I passed by the Masjid when the people
were absorbed in story-telling. So I entered upon 'Ali and said: 'O
Commander of the believers! Do you not see the people are becoming
engrossed in story-telling?' He said: 'They have been consumed with
it?' I said: "Yes.' He said: 'As for me, I heard the Messenger of
Allah (ﷺ) saying: "Indeed there comes a Fitnah" So I said: "What is
the way out from it O Messenger of Allah?" He said: "Allah's book. In
it is news for what happened before you, and information about what
comes after you, and judgement for what happens between you. It is the
Criterion (between right and wrong) without jest. Whoever among the
oppressive abandons it, Allah crushes him, and whoever seeks guidance
from other than it, then Allah leaves him to stray. It is the firm
rope of Allah, it is the wise remembrance, it is the straight path,
and it is the one that the desires can not distort, nor can the
tongues twist it, nor can the scholars ever have enough of it, and it
shall not become dull from reciting it much, and the amazement of it
does not diminish. It is the one that when the Jinns hear it, they did
not hesitate to say about it: 'Verily, we have heard a wonderful
Recitation (this Qur'an)! 'It guides to the Right Path, and we have
believed therein.' Whoever speaks according to it then he has said the
truth, and whoever acts according to it he is rewarded, and whoever
judges by it he has judged justly, and whoever invites to it then he
guides to the straight path." Take this O A'war!'."
[Jami' at-Tirmidhi]
حَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، حَدَّثَنَا حُسَيْنُ بْنُ عَلِيٍّ
الْجُعْفِيُّ، قَالَ سَمِعْتُ حَمْزَةَ الزَّيَّاتَ، عَنْ أَبِي
الْمُخْتَارِ الطَّائِيِّ، عَنِ ابْنِ أَخِي الْحَارِثِ الأَعْوَرِ، عَنِ
الْحَارِثِ، قَالَ مَرَرْتُ فِي الْمَسْجِدِ فَإِذَا النَّاسُ يَخُوضُونَ
فِي الأَحَادِيثِ فَدَخَلْتُ عَلَى عَلِيٍّ فَقُلْتُ يَا أَمِيرَ
الْمُؤْمِنِينَ أَلاَ تَرَى أَنَّ النَّاسَ قَدْ خَاضُوا فِي
الأَحَادِيثِ . قَالَ وَقَدْ فَعَلُوهَا قُلْتُ نَعَمْ . قَالَ أَمَا
إِنِّي قَدْ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ "
أَلاَ إِنَّهَا سَتَكُونُ فِتْنَةٌ " . فَقُلْتُ مَا الْمَخْرَجُ
مِنْهَا يَا رَسُولَ اللَّهِ قَالَ " كِتَابُ اللَّهِ فِيهِ نَبَأُ مَا
كَانَ قَبْلَكُمْ وَخَبَرُ مَا بَعْدَكُمْ وَحُكْمُ مَا بَيْنَكُمْ هُوَ
الْفَصْلُ لَيْسَ بِالْهَزْلِ مَنْ تَرَكَهُ مِنْ جَبَّارٍ قَصَمَهُ
اللَّهُ وَمَنِ ابْتَغَى الْهُدَى فِي غَيْرِهِ أَضَلَّهُ اللَّهُ وَهُوَ
حَبْلُ اللَّهِ الْمَتِينُ وَهُوَ الذِّكْرُ الْحَكِيمُ وَهُوَ
الصِّرَاطُ الْمُسْتَقِيمُ هُوَ الَّذِي لاَ تَزِيغُ بِهِ الأَهْوَاءُ
وَلاَ تَلْتَبِسُ بِهِ الأَلْسِنَةُ وَلاَ يَشْبَعُ مِنْهُ الْعُلَمَاءُ
وَلاَ يَخْلَقُ عَلَى كَثْرَةِ الرَّدِّ وَلاَ تَنْقَضِي عَجَائِبُهُ
هُوَ الَّذِي لَمْ تَنْتَهِ الْجِنُّ إِذْ سَمِعَتْهُ حَتَّى قَالُوا
(إِنَّا سَمِعْنَا قُرْآنًا عَجَبًا * يَهْدِي إِلَى الرُّشْدِ )
مَنْ قَالَ بِهِ صَدَقَ وَمَنْ عَمِلَ بِهِ أُجِرَ وَمَنْ حَكَمَ بِهِ
عَدَلَ وَمَنْ دَعَا إِلَيْهِ هُدِيَ إِلَى صِرَاطٍ مُسْتَقِيمٍ " .
خُذْهَا إِلَيْكَ يَا أَعْوَرُ .
قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ لاَ
نَعْرِفُهُ إِلاَّ مِنْ هَذَا الْوَجْهِ وَإِسْنَادُهُ مَجْهُولٌ .
وَفِي الْحَارِثِ مَقَالٌ .
He also quoted that it is the Messenger of Allah Muhammed (peace be upon him) and his two followers Abu Bakr and Omar (may Allah be pleased with them).
Then he summarized that all these have the same meaning as Muhammad (peace be upon him) came with the true faith (Islam) and the Quran and those who follow him follow this faith and book etc.
Just as reference for what has been said in at-tahrir wa at-tanwir
Also in Jami' at-Tirmidi and Musnad al Imam Ahmad you can find the Hadith:
Narrated An-Nawwas bin Sam'an Al-Kilabi: that the Messenger of Allah
(ﷺ) said: "Indeed Allah has made a parable of the straight path: At
the sides of the path there are walls with open doors, each door
having a curtain. There is a caller at the head of the path calling,
and a caller above it calling. And Allah invites to the abode of peace
and guides whomever He wills to the straight path. The doors which are
on the sides of the path are the Hudud (legal limitations) of Allah;
no one breaches the Hudud of Allah except that curtain is lifted, and
the one calling from above it is his Lord."
حَدَّثَنَا عَلِيُّ بْنُ حُجْرٍ السَّعْدِيُّ، حَدَّثَنَا بَقِيَّةُ بْنُ
الْوَلِيدِ، عَنْ بَحِيرِ بْنِ سَعْدٍ، عَنْ خَالِدِ بْنِ مَعْدَانَ،
عَنْ جُبَيْرِ بْنِ نُفَيْرٍ، عَنِ النَّوَّاسِ بْنِ سَمْعَانَ
الْكِلاَبِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم "
إِنَّ اللَّهَ ضَرَبَ مَثَلاً صِرَاطًا مُسْتَقِيمًا عَلَى كَنَفَىِ
الصِّرَاطِ دَارَانِ لَهُمَا أَبْوَابٌ مُفَتَّحَةٌ عَلَى الأَبْوَابِ
سُتُورٌ وَدَاعٍ يَدْعُو عَلَى رَأْسِ الصِّرَاطِ وَدَاعٍ يَدْعُو
فَوْقَهُ: (وَاللَّهُ يَدْعُو إِلَى دَارِ السَّلاَمِ وَيَهْدِي مَنْ
يَشَاءُ إِلَى صِرَاطٍ مُسْتَقِيمٍ) وَالأَبْوَابُ الَّتِي عَلَى
كَنَفَىِ الصِّرَاطِ حُدُودُ اللَّهِ فَلاَ يَقَعُ أَحَدٌ فِي حُدُودِ
اللَّهِ حَتَّى يُكْشَفَ السِّتْرُ وَالَّذِي يَدْعُو مِنْ فَوْقِهِ
وَاعِظُ رَبِّهِ " . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ
غَرِيبٌ . قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ عَبْدِ الرَّحْمَنِ
يَقُولُ سَمِعْتُ زَكَرِيَّا بْنَ عَدِيٍّ يَقُولُ قَالَ أَبُو إِسْحَاقَ
الْفَزَارِيُّ خُذُوا عَنْ بَقِيَّةَ مَا حَدَّثَكُمْ عَنِ الثِّقَاتِ
وَلاَ تَأْخُذُوا عَنْ إِسْمَاعِيلَ بْنِ عَيَّاشٍ مَا حَدَّثَكُمْ عَنِ
الثِّقَاتِ وَلاَ غَيْرِ الثِّقَاتِ .
Version of at-Tirmidhi
حدثنا الحسن بن سوار أبو العلاء
حدثنا ليث يعني ابن سعد ، عن معاوية بن صالح : أن عبد الرحمن بن جبير بن
نفير ، حدثه عن أبيه ، عن النواس بن سمعان ، عن رسول الله صلى الله عليه
وسلم قال : ضرب الله مثلا صراطا مستقيما ، وعلى جنبتي الصراط سوران فيهما
أبواب مفتحة ، وعلى الأبواب ستور مرخاة ، وعلى باب الصراط داع يقول : يا
أيها الناس ، ادخلوا الصراط جميعا ولا تعوجوا ، وداع يدعو من فوق الصراط
، فإذا أراد الإنسان أن يفتح شيئا من تلك الأبواب ، قال : ويحك ، لا
تفتحه ؛ فإنك إن تفتحه تلجه . فالصراط الإسلام ، والسوران حدود الله ،
والأبواب المفتحة محارم الله ، وذلك الداعي على رأس الصراط كتاب الله ،
والداعي من فوق الصراط واعظ الله في قلب كل مسلم .
[Version of Imam Ahmad]
p.s.: Ibn Kathir quoted the Version of Imam Ahmad!
