Ahmad, Muslim, Abu Dawud, and al-Baihaqi record that Yahya ibn Yazid said:
"I asked Anas ibn Malik about shortening the prayer, and he said:
'The Messenger of Allah would pray two rak'at if he had traveled a distance of three miles or farsakh."'
Ibn Hajar writes in Fath al-Bari:
"This is the most authentic hadith which states and clarifies [that question]." The conflict between mile and farsakh is made clear in Abu Sa'id al-Khudri's statement:
"If the Prophet traveled a distance of one farsakh, he would shorten his prayer." This was related by Sa'id ibn Mansur in his Sunan and by al-Hafiz ibn Hajar in at-Talkhis, and he implicitly accepted it by not making any further comments about it. It is well-known that a farsakh equals three miles and, therefore, Abu Sa'id's hadith removes the confusion which arises from Anas' hadith when he says that the shortest distance, due to which the Prophet shortened his prayer, was three miles. One farsakh is equivalent to 5,541 meters while one mile equals 1,748 meters. The shortest distance which has been mentioned with respect to the shortening of salah is one mile. This was recorded by Ibn abi Shaibah, with a sahih chain, on the authority of Ibn 'Umar. Ibn Hazm follows this report, and argues that if the distance is less than one mile, one is not to shorten the salah, the Messenger of Allah went to the graveyard of al-Baqi' to bury the dead and (similarly) he went off to answer the call of nature and did not shorten his salah.
Concerning what some jurists say, namely, that the journey must be at least two days long or as some say three days, Imam Abu al-Qasim alKharqi's refutation of their opinion is sufficient for us. In al-Mughni he says: 'I do not find any proof for what those scholars say. The statements of the (sahabah) companions are contradictory, and they are not a (conclusive) proof if they differ. Something has been related from Ibn 'Umar and Ibn 'Abbas which differs from what these scholars use as proof. Even if that were not the case, their statements do not constitute a proof when a statement or action of the Prophet himself exists. Even if their statements were accepted, we would not be able to follow the distance they mentioned due to the following two reasons. One, they differ from the sunnah that has been related from the Prophet and from the clear meaning of the Qur'an, as the clear meaning of the verse allows one to shorten one's salah if one makes any journey upon the earth.
Allah says: "If you journey on the earth, there is no blame upon you if you shorten your prayer."
The condition of there being fear has been deleted as can be seen in the hadith we recorded from Ya'la ibn Umayyah, and what remains is the clear meaning of the verse which covers every type of journey. The Prophet said:
"The traveler may wipe over his socks for a period of three days."
This shows the length of time that one may wipe over the socks and it cannot be used as a proof for the question we are discussing here. One could argue that traveling is less than a three-day journey on the basis of the hadith:
"It is not allowed for any woman who believes in Allah and the last day to travel a journey of one day, save in the presence of a male relative."
Two, the question of the distance to be traveled is one that may only be answered by some sort of revelation from Allah, the Exalted [the Qur' an or Sunnah]; it is not the type of issue which one may address on the basis of personal reasoning, nor is there any way to derive an analogy. The proofs w hich exist support the opinion that shortening the salah is permissible for every traveler, unless there is some consensus to the contrary."
Similar to that is the traveling by planes, trains, and so forth, or a trip that is in obedience to Allah, the Exalted, or otherwise. If there is someone whose occupation requires him to always be traveling, for instance, a pilot, a ship captain, truck driver, and so on, then he is permitted to shorten his salah or break his fast as he is truly traveling.
http://www.islamawareness.net/Salah/...us_sunnah.html