بسم الله الرحمن الرحيم
[The following is translated from the Kuwaiti Fiqh Encyclopedia]:
“The vast majority of the scholars namely the Malikiyah, Shafi’iyyah and Hanabilah are of the opinion that the distance of travel by which the laws (like qasr) changes is four (4) burud. This is based on the hadith related by Ibn Abbas (رضي الله عنهما) that the Prophet (صلى الله عليه وسلم) said, “O people of Makkah, do not shorten your Salah in less than four burud, from Makkah to U’sfaan.” Ibn Umar (رضي الله عنهما) and Ibn Abbas (رضي الله عنهما) used to shorten their Salah and leave fasting in four burud[‘s travel]. That could only be practiced if heard from the Messenger (صلى الله عليه وسلم).
Each barid (singular of burud) is four farasikh. A farsakh is three Hashimi miles. The total is 48 Hashimi miles.
[Based on this the distance which permit shortening the Salah is approximately 77 kilometers.][i]
The Hanafiyah are of the opinion that the distance of travel by which the laws (like qasr) are changed is three days travel.”
[Mawsu’ah Fiqhiyah Vol.25 Pg.28-29]
The later Hanafi scholars calculated this to be equivalent to 48 miles which is equal to 77.5 kilometers.
[i] Footnote of Mawsu’ah Vol.25 Pg.29 Ta’leeq (1)