Generally speaking, shortening the Prayer and breaking the fast of Ramadan while traveling are two legal concessions that portray Islam’s tolerance and simplicity in matters of worship. The Prophet used to shorten his Prayer whenever he was on a journey. He (peace and blessings be upon him) said: “Allah likes His servants to undertake the legal concessions given to them in the same way as He likes them to observe their obligations.”
Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, states: It is well known that shortening Prayer is a legal concession given to a traveler, as Allah Almighty says: (And when ye go forth in the land, it is no sin for you to curtail (your) worship if ye fear that those who disbelieve may attack you.) (An-Nisaa’: 101) Breaking the fast of Ramadan is another concession for the traveler; Allah Almighty says: (…And whosoever of you is sick or on a journey, (let him fast the same) number of other days.) (Al-Baqarah: 185) Moreover, Abu Dawud reported the Prophet (peace and blessings be upon him) as saying: “Allah has relieved a traveler from (the obligatory) fasting (in Ramadan) and half of the Prayers.” These concessions apply on fulfilling all the conditions that make a Muslim worthy of such concessions, as agreed by Muslim jurists.
Travel may be temporary or permanent. Permanent travel is one of two cases. The first case is that of a person who accompanies his family and all his needs in his travel [such as a nomad], and the second is a person who doesn’t accompany his family, but his work requires him to constantly travel, such as the train engineers, pilots, and sailors.
A person whose travel is temporary has a legal concession to shorten Prayer and break the fast of Ramadan. But the one who travels along with his family and their requirements [such as a nomad] is considered a resident of the place he travels to and, thus, he is not allowed neither to shorten Prayer nor break the fast of Ramadan, unless fasting really endangers his health. If it is so, he can break his fast. Breaking the fast of Ramadan may sometimes be obligatory if fasting leads one to his ruin.
It is recorded in Al-Mughni by Ibn Qudamah, in the section on Hanbali fiqh: Al-Athram said: I heard Abu `Abdullah Ahmad ibn Hanbal being asked whether a sailor is allowed to shorten Prayer and break the fast of Ramadan when he is on board the ship. He answered: “If the ship is his home, then he is to perform all the Rak`ahs of Prayer without shortening and fast in Ramadan.” He was asked: “How can the ship be his home?” He answered: “That he has no other residence, and he and his family live on it.” `Ata’ also has the same opinion.
In Sharh Ash-Sharqawi `ala At-Tahrir, in the section on Shafi`i fiqh: It is not permissible for a person who travels constantly to break the fast of Ramadan, for this means abandoning the obligatory fasting of Ramadan completely, unless he intends to make up for the broken fast days on other days during his travel. But a person who travels a lot alone due to his job requirements is permitted to shorten Prayer and break the fast of Ramadan. This is because such a man necessarily spends some days at home. Hence he can make up for the broken fast days of Ramadan. The Hanafi scholars of fiqh maintain that shortening Prayer in this case is the original rule, and whoever performs Prayers fully has no right to combine them. (Fatawa Sheikh Gadul-Haqq)