✅Answer: Please pay attention to the following narrations:

1 الْفَضْلِ بْنِ شَاذَانَ عَنِ الرِّضَا فِي كِتَابِهِ إِلَى الْمَأْمُونِ وَ التَّقْصِيرُ فِي ثَمَانِيَةِ فَرَاسِخَ وَ مَا زَادَ وَ إِذَا قَصَّرْتَ أَفْطَرْتَ

📚 Uyun Akhbar al-Reza, vol. 2, page 123

Imam Reza (peace be upon him) said: 'The shortening of the prayer is at 8 parasangs or more, and when you shorten the prayer, you also break your fast!'

2 عَنِ الْفَضْلِ بْنِ شَاذَانَ عَنِ الرِّضَا أَنَّهُ سَمِعَهُ يَقُولُ إِنَّمَا وَجَبَ التَّقْصِيرُ فِي ثَمَانِيَةِ فَرَاسِخَ لَا أَقَلَّ مِنْ ذَلِكَ وَ لَا أَكْثَرَ لِأَنَّ ثَمَانِيَةَ فَرَاسِخَ مَسِيرَةُ يَوْمٍ لِلْعَامَّةِ وَ الْقَوَافِلِ وَ الْأَثْقَالِ

📚 Al-Faqih, vol. 1, page 454

Imam Reza (peace be upon him) said: 'Indeed, shortening the prayer is obligatory at 8 parasangs, neither less nor more, because 8 parasangs is the measure of one day's journey for the common people, caravans, and camels with loads!'

3 عَبْدِ اللَّهِ بْنِ يَحْيَى الْكَاهِلِيِّ أَنَّهُ سَمِعَ الصَّادِق يَقُولُ فِي التَّقْصِيرِ فِي الصَّلَاةِ بَرِيدٌ فِي بَرِيدٍ أَرْبَعَةٌ وَ عِشْرُونَ مِيلًا ثُمَّ قَالَ كَانَ أَبِي يَقُولُ إِنَّ التَّقْصِيرَ لَمْ يُوضَعْ عَلَى الْبَغْلَةِ السَّفْوَاءِ وَ الدَّابَّةِ النَّاجِيَةِ وَ إِنَّمَا وُضِعَ عَلَى سَيْرِ الْقِطَار

📚 Faqih, vol. 1, page 436

Kahili heard from Imam Sadiq (peace be upon him) regarding the shortening of the prayer: 'A barid (i.e., 4 parasangs of going) in a barid (4 parasangs of returning), which is 24 miles!'

Then he said: 'My father used to say: 'The shortening of the prayer was not based on a swift mule or a fast mount, but rather it was based on the movement of camels that travel one after another!'

4 عَنْ سَمَاعَةَ قَالَ: سَأَلْتُهُ عَنِ الْمُسَافِرِ فِي كَمْ يُقَصِّرُ الصَّلَاةَ فَقَالَ فِي مَسِيرَةِ يَوْمٍ وَ ذَلِكَ بَرِيدَانِ وَ هُمَا ثَمَانِيَةُ فَرَاسِخ

📚 Al-Tahdhib, vol. 3, page 207

Sama'a said: I asked (Imam Sadiq, peace be upon him) about a traveler: 'At what distance does he shorten the prayer?' He said: 'At a day's journey, which is two barids, and that is 8 parasangs!'

5 عَبْدِ الرَّحْمَنِ بْنِ الْحَجَّاجِ عَنْ أَبِي عَبْداللَّه فِي حَدِيثٍ قَالَ: قُلْتُ لَهُ كَمْ أَدْنَى مَا يُقَصَّرُ فِيهِ الصَّلَاةُ قَالَ جَرَتِ السُّنَّةُ بِبَيَاضِ يَوْمٍ فَقُلْتُ لَهُ إِنَّ بَيَاضَ يَوْمٍ يَخْتَلِفُ يَسِيرُ الرَّجُلُ خَمْسَةَ عَشَرَ فَرْسَخاً فِي يَوْمٍ وَ يَسِيرُ الْآخَرُ أَرْبَعَةَ فَرَاسِخَ وَ خَمْسَةَ فَرَاسِخَ فِي يَوْمٍ قَالَ فَقَالَ إِنَّهُ لَيْسَ إِلَى ذَلِكَ يُنْظَرُ أَ مَا رَأَيْتَ سَيْرَ هَذِهِ الْأَمْيَالِ(الأثقال) بَيْنَ مَكَّةَ وَ الْمَدِينَةِ- ثُمَّ أَوْمَأَ بِيَدِهِ أَرْبَعَةً وَ عِشْرِينَ مِيلًا يَكُونُ ثَمَانِيَةَ فَرَاسِخَ

📚 Tahdhib, vol. 4, page 222

Abd al-Rahman said: I said to Imam Sadiq (peace be upon him): 'What is the shortest distance for which the prayer is shortened?'

He said: 'The tradition has been established on a day's daylight!' (i.e., the distance that can be traveled from sunrise to sunset)

So I said: 'A day's daylight varies: one person travels 15 parasangs in a day, and another 4 parasangs and 5 parasangs!'

The Imam said: 'Certainly, this matter is not considered (this is not the criterion), have you not seen the journey of these camels with loads between Mecca and Medina?!'

Then the Imam pointed with his hand to 24 miles, which is 8 parasangs!

✅ Although the criterion of 'yaum' (a day), meaning the distance traveled in one day, and others, have been set as the measure for the distance of shortening the prayer in the above narrations and others, it is completely clear that this criterion is based on the journey and movement of camels with loads, who travel 8 parasangs in one day, and not other vehicles.

Some, based on today's fast-moving vehicles such as airplanes, without paying close attention to the narrations, have returned to the criterion of 'biyaad yaum' (a day's daylight) and 'yaum' (a day), and according to that, if someone travels by airplane, train, or fast car, they consider a day's travel as the criterion for shortening the prayer and do not consider less than that to be a reason for shortening the prayer, which is a very clear mistake. This is because even during the time of the Ahl al-Bayt (peace be upon them), different mounts would travel different distances in one day, and the Imam explicitly says that this matter is not considered in this case. Rather, the distance a camel with a load travels in a day, which is 8 parasangs, is the criterion for shortening the prayer and breaking the fast. If someone's travel distance is this much, their prayer is shortened and their fast is broken, even if they cover this distance in a few minutes by helicopter, fast car, or airplane.