Ibn Bābawayh reports from Zurāra and Muḥammad b. Muslim a report wherein 2 Barīds is the distance given for beginning to shorten your prayer.
رُوِيَ عَنْ زُرَارَةَ وَ مُحَمَّدِ بْنِ مُسْلِمٍ أَنَّهُمَا قَالا: قُلْنَا لِأَبِي جَعْفَرٍ ع: مَا تَقُولُ فِي الصَّلَاةِ فِي السَّفَرِ كَيْفَ هِيَ؟ وَكَمْ هِيَ؟ ... وَقَدْ سَافَرَ رَسُولُ اللَّهِ ص إِلَى ذِي خُشُبٍ وَهِيَ مَسِيرَةُ يَوْمٍ مِنَ الْمَدِينَةِ يَكُونُ إِلَيْهَا بَرِيدَانِ أَرْبَعَةٌ وَ عِشْرُونَ مِيلًا فَقَصَّرَ وَأَفْطَرَ فَصَارَتْ سُنَّةً ...
Ṭūsī reports from Muḥammad b. Muslim that Friday prayer is obligatory when they reach 7 in number
وَرَوَى مُحَمَّدُ بْنُ مُسْلِمٍ عَنْ أَبِي جَعْفَرٍ ع قَالَ: تَجِبُ الْجُمُعَةُ عَلَى سَبْعَةِ نَفَرٍ مِنَ الْمُؤْمِنِينَ وَلَا تَجِبُ عَلَى أَقَلَّ مِنْهُمُ: الْإِمَامُ وَقَاضِيهِ وَمُدَّعِيَا حَقٍّ وَشَاهِدَانِ وَالَّذِي يَضْرِبُ الْحُدُودَ بَيْنَ يَدَيِ الْإِمَام
But this is not contradictory with 5 since in another report we learn that the Imams would say 7 first and then drop it to 5 (which some jurists have interpreted as wujūb and istiḥbāb respectively).
الْحُسَيْنُ بْنُ مُحَمَّدٍ عَنْ عَبْدِ اللَّهِ بْنِ عَامِرٍ عَنْ عَلِيِّ بْنِ مَهْزِيَارَ عَنْ فَضَالَةَ عَنْ أَبَانِ بْنِ عُثْمَانَ عَنْ أَبِي الْعَبَّاسِ عَنْ أَبِي عَبْدِ اللَّهِ ع قَالَ: أَدْنَى مَا يُجْزِئُ فِي الْجُمُعَةِ سَبْعَةٌ أَوْ خَمْسَةٌ أَدْنَاهُ
8. The incredible thing is that both answers have not changed from that day when Muḥammad b. Ḥukaym confronted Sharīk in the orchard to this day of ours. It is the famous position of all our jurists that one should begin to shorten prayer after travelling 8 farsakh (= 2 barīds) (https://www.sistani.org/english/book/48/2264/) and that Friday prayer becomes obligatory when they reach 5 men including the Imam (https://www.sistani.org/english/book/48/2210/).
So much for the Imami madhhab not being preserved!
9. Sharīk thought that if the questions were in ṣalāt they would be easy to answer but alas it was not to be so! He is commended, however, for realizing the momentous gravity of making up a Prophetic report on the spot, and acknowledging that he did not know the answer to both issues.
This is a far cry from other jurists who are known to have made up Prophetic reports to support the legal position they were inclined to. As a famous fabricator put it:
كنا إذا رأينا رأيًا، جعلنا له حديثًا
This is a known phenomenon which Sunni scholars had to contend with.
10. Muḥammad b. Muslim had a reputation for three things: Having a long beard, being truthful, being a kashshābī.
Those were the days when the Shia were the forefront in applying the sunna. If one has a long beard today he would be deemed as belonging to some other sect (which need not be named)
Khashābī originated as a label for the mainly Persian mawālī followers of Mukhtār who joined his insurrection in Kūfa, this was because wooden clubs were the main weapons used by this economically disadvantaged segment who could not afford more conventional weapons before becoming a wider derogatory term for the Rāfiḍa as a whole.
In conclusion: The fact that there is external corroboration for numerous points found in this report not to speak its internal coherence gives confidence that we are dealing with a historical event.