Hadith.1318 - Al-Fadl ibn Shadhan al-Naysaburi, may Allah (swt) have mercy on him, mentioned among the reasons he heard from al-Ridha (as) regarding why prayers are shortened during travel. He (Imam (as)) said: "The initially prescribed obligatory prayer was ten rak'ahs. The seven additional rak'ahs were later added, and Allah (swt), the Blessed and Exalted, lightened this addition for the servant due to the burden, fatigue, and preoccupation of travel. This relief was granted so that the servant would not become distracted from the essential needs of their livelihood during travel. However, the Maghrib prayer is not shortened because it was originally set as a shortened prayer. The obligation to shorten applies to eight farsakhs (a day's journey) and no less. The reason for this is that eight farsakhs is a day’s journey for the common people, caravans, and baggage carriers, necessitating shortening for such a journey. If the obligation were not established for a day’s journey, it would not be required for a journey of a thousand years, as every day after this day is similar to it ; if it were not obligatory for this day, it would not be obligatory for its equivalent. Voluntary prayers during the day are omitted while traveling, but not voluntary prayers at night, because every prayer that is not shortened also maintains its voluntary aspect. Thus, the Maghrib prayer is not shortened, so neither are the voluntary prayers that follow it. Similarly, the Fajr prayer is not shortened, so neither are the voluntary prayers preceding it. The Isha prayer (Atamah) is considered shortened, but its two rak'ahs are not omitted because they are not part of the fifty obligatory rak'ahs; rather, they are additional voluntary rak'ahs to complete the fifty. These extra rak'ahs serve as compensation, with two voluntary rak'ahs taking the place of every rak'ah of obligation. The traveler and the sick are permitted to perform the night prayer at the beginning of the night due to their preoccupation, weakness, or to ensure they fulfil their prayers and gain rest or focus on their travel."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.

Hadith.1319 - Sa'id ibn al-Musayyib asked Ali ibn al-Hussain (as), "When was the prayer made obligatory upon the Muslims in the form it is today?" He (as) replied: "In Medina, when the call (to Islam) became manifest, Islam was strengthened, and Allah (swt), the Mighty and Majestic, prescribed jihad upon the Muslims. The Messenger of Allah (sw) added seven rak'ahs to the prayers: two to Dhuhr, two to Asr, one to Maghrib, and two to the Isha prayer, while leaving the Fajr prayer as it had been prescribed in Mecca. This was to hasten the ascent of the night’s angels to the heavens and the descent of the day’s angels to the earth. Thus, the angels of the night and the angels of the day would witness the Fajr prayer with the Messenger of Allah (sw). This is why Allah (swt), Blessed and Exalted, said: 'Recite the Qur'an at dawn. Indeed, the recitation of the Qur'an at dawn is ever witnessed' (Qur'an 17:78) — witnessed by the Muslims and by the angels of the night and the angels of the day."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.