The Shari'ah has allowed the traveller to shorten his prayer while on journey, and to offer only two rak'ahs of Fard at a prayer time where one has normally to offer four rak'ahs.

The Qur'an says: " When you go on a journey, there is no harm if you shorten Salat." [Qur'an 4:101]

The holy Prophet has said: "This is a favour of Allah to you, so you should accept His favour gratefully." (Bukhari, Muslim, Tirmidhi)

Injunction Concerning Shortening the Prayer

After a person has left his habitation with the intention of proceeding on journey, he should shorten his prayer, otherwise he would be committing a sin. ('Ilm al-Fiqh, Vol. II, p. 130, Durr al-Mukhtar, etc.)

Hadrat Abdullah ibn Umar says: "I have travelled in company with the holy Prophet, Abu Bakr, Umar and Uthman, and have never seen them offering more than two rak'ahs of Fard during a journey." (Bukhari, Muslim)

It should be borne in mind that shortening is allowed only in those prayers were one has normally to offer four rak'ahs of Fard namely Zuhr, Asr and Isha prayers. In the Fajr and Maghrib prayers, no shortening is allowed, and one has to offer two and three rak'ahs of Fard respectively.

Injunction about the Sunnat and Nafl Prayer

The Sunnat rak'ahs of the Fajr prayer should not be abandoned and as far as possible, one should also offer the Sunnat rak'ahs of Maghrib. But as for the Sunnat rak'ahs of the other prayers, one has complete option. One should offer only Fard rak'ahs, when one is actually travelling, but when one has halted at a place during the journey one may offer the Sunnat rak'ahs as well (Durr al-Mukhtar). The Witr prayer, however, being Wajib must be offered in full. No shortening is allowed in the Sunnat or Nafl rak'ahs during the journey. If a person chooses to offer them, he has to offer them in full. 

Mileage of the Journey
If a person sets out with the intention of visiting a place that is about 36 miles⁽¹⁾ away from his hometown, he will be considered to be on a journey. This distance can be covered in three days by a person who walks a normal gait and who travels from morning until the sun begins to decline. It does not matter whether a person covers this distance on foot in three days or reaches his destination by a faster mode of conveyance in a few hours, he might shorten his prayer during the journey.

When to Shorten the Prayer

After one has set out on journey, one should continue offering the prayer in full as long as one is inside the habitation. But as soon as one has crossed the outer-most limits of the habitation, one may begin shortening the prayer.

The Period of Qasr

The traveller is allowed to continue shortening the prayer until he returns home. However, if during the journey, he makes up his mind to halt at a place for 15 days or more, he will be regarded as being at home and will have to offer the full prayers no matter whether he has to cut short his stay later due to some reason. On the other hand, if he has the intention of staying for less than 15 days at a place, he will shorten his prayers as if on a journey, and will continue doing so even if he has to prolong his stay for months and has to postpone his departure, due to unforeseen circumstances (provided that he intends to stay for less than 15 days each time).

Miscellaneous Regulations Concerning Qasr

1. If a traveller offers four rak'ahs of Fard by mistake, and has observed the first Qa'dah duly after two rak'ahs, he should perform sajdah sahv. In this case, two of the four rak'ahs will be regarded as Fard and the remaining two as Nafl and the prayer will be in order. However, if he has not observed the first Qa'dah, the four rak'ahs will be counted as Nafl, and he will have to offer the prayer afresh.

2. If a person has an itinerary of staying various numbers of days at different places, i.e. five days here and ten days there, but less than 15 days in each case, he will have to shorten his prayers throughout the journey.

3. If a married woman has started living permanently with her husband, her home will be the home of her husband. Now if she undertakes a journey to visit her parents, who live at least 36 miles away, she will have to shorten prayers at the parents' home. However if she has gone to stay with her husband for a few days and she has the intention of living with her parents most of the time, her home will be the home of her parents.

4. If a woman is travelling with her husband, or a servant with his master, or a boy with his father, or a ward with his guardian, their intention will not be reliable. Even if the woman, or the servant, or the boy makes up his or her mind to stay at a place for more than 15 days, he or she will not be regarded as resident unless it is also the intention of the husband or the master himself.

5. The residence of the place can offer their prayer behind an Imam who is travelling. Such an Imam, however, has to announce after salutation at the completion of two Rak'ahs that he is a traveller so the resident followers may complete their prayer independently.

6. A traveller can offer his prayer behind a resident Imam, though in this case he has to observe the full prayer in obedience to the Imam and is not allowed to shorten it.

7. If a person has not yet made up his mind about the duration of his stay, or has the intention of staying for less than 15 days at a place, but then during the prayer he changes his mind to extend his stay to 15 days or more, he will have to offer the full prayer and will no longer be allowed shorten it.

8. The prayers missed during a journey will have to be shortened when offered later at home, and the prayers missed while at home will have to be offered in full when offered during a journey.

Combining Two Prayers during a Journey

Combining two prayers during the Hajj and offering them together is in accordance with the Sunnah of the holy Prophet. The Zuhr and Asr prayers are combined on the 9^th Zul-Hijjah at the plain of 'Arafah, and offered at the Zuhr time with one Azan but two separate Iqamahs.⁽²⁾After sunset the pilgrims leave for Muzdalifah and combine the Maghrib and Isha prayers there. If a person offers his Maghrib prayer on the way to Muzdalifah, his prayer will not be valid and he will have to offer it afresh.

Combining two prayers together except during Hajj is not permissible, though one may combine them apparently by offering one prayer just after the other. One may, for instance, delay a prayer up to its last time limit and offer the other at the beginning of its time limit. In this way, the prayers would apparently seem to have been combined, but actually they are not combined but offered within their own prescribed time limits.⁽³⁾

2. A separate Iqamah for the Asr prayer is necessary so that people may know that the prayer is being offered before its prescribed time on the 9^th Zul-Hijjah.

3.According to the Ahl al-Hadith, combining of two prayers together is permissible during every journey, not only apparently but actually as well. In other words, one may combine the prayers and offer them actually together at a prescribed time during the journey. This may be done in two ways:

(a) The later prayer may be offered before it's time along with and during the time limit of an earlier prayer. For instance, Asr prayer may be offered along with a Zuhr prayer in after the sun has declined. This is termed Jamm'i-Taqdim, i.e. combining the prayers at the time of the earlier prayer.

(b) The earlier prayer may be delayed and offered along with and during the time limit of the later prayer. For instance, the Zuhr prayer may be delayed and offered along with the Asr prayer after the sun has declined. This is termed Jamm'i-Takhir, i.e. combining the prayers at the time of the later prayer.

Hadrat ibn Abbas says, "The practice of the holy Prophet was that before starting on any journey, if he saw that the sun has declined, he would first offer the Zuhr and Asr prayers at the Zuhr time and then set out on the journey. On the other hand if he saw that the sun had not yet declined, he would set out on the journey and combine the Zuhr and Asr prayers on the way at the Asr time. Similarly if he saw that the sun had set, he would combine the Maghrib and Isha at home and then start out on the journey. But if the sun had not yet set, he would set out and combine the Isha and Maghrib prayers on the way at the Isha time." (Musnad Ahmad)

And Hadrat Mu'az bin Jabal has reported that during the Tabuk Campaign, if the holy Prophet resumed the journey before the sun had declined, he would combine the Zuhr and Asr prayers at the Asr time, but if the sun had declined, he would first offer the Zuhr and Asr prayers at the Zuhr time and then resume the journey. Similarly if he resumed the journey before the setting of the sun, he would combine the Maghrib and Isha prayers at the Isha time, but if he started after sunset, he would combine the Maghrib and Isha prayers at the Maghrib time and then resume the journey." (Tirmidhi)