I recently came across this piece of information and thought it would be nice to share it.  Qasr - Shortening of prayer

Qasr is the shortening of prayer that consist of four rakaats, where the rakaats are shortened to two. This is only applicable to Dhuhr, Asr and Isha' prayers. It is not permissible to shorten Maghrib or Subuh prayers which consist of three and two rakaats respectively.

The practice of qasr is permissible based on the following:

"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. In truth the disbelievers are an open enemy to you. (Q4V101)

"Ya'la ibn Umaiyyah said: "I said to 'Umar ibn al-Khattab: "Explain to me why the people shorten the salah when Allah says, 'And when you go forth...[the preceding verse] and those days are gone now!' 'Umar said: 'I wondered about that too and I mentioned that to the Prophet and he said: "This is a charity that Allah, the Exalted, has bestowed upon you, so accept His charity.'"(Al-Nasai' and Abu Daud)

Distance for the Qasr to be permissible

The minimum distance travelled in order for it to be permissible for prayers to be shortened is two marhalahs, which is four burudins. One burudin consists of four farsakhs and each farsakh is 5.514km under the metric system. Two marhalahs therefore is approximately 89 km.

Stipulations of Qasr

1. The journey should be one that is permissible according to the Shariah. 2. The distance of the journey should not be less than two marhalahs (89km / 56 miles). 3. There must be niyyat (expression of intent) to qasr (shorten) the prayer during the takbiratul ihram. 4. When praying in congregation, the imam must not be someone performing the full prayer. 5. The shortened prayer should be that of a prayer that consist of 4 rakaats (Dhuhr, Asr or Isha').

Example of Niyyat

أصلي فرض الظهرركعتين قصرالله تعالى

(I am making niyyah to pray Dhuhr qasr to two rakaats, for Allah Taa'la)

Jama' - The Combining of prayers

There are two types of Jama' that is permissible:

Jama' Taqdim which refers to the combination of two prayers into the earlier time, such as combining Dhuhr and 'Asr and performing it during Dhuhr, or combining Maghrib and Isha' and performing it during Maghrib. Jama' Ta'khir which refers to the combination of two prayers into the later time, such as combining Dhuhr and 'Asr and performing it during 'Asr, or combining Maghrib and Isha' and performing it during Isha'.

Rules for Jama' Taqdim

1. The prayer should be done in order, which means the Dhuhr is performed before the 'Asr or the Maghrib is performed before the Isha'. 2. Niyyat (expression of intent) should be in the first prayer before the giving of the salaam, although it is best done during the takbiratul ihram. 3. The second prayer must immediately follow the earlier prayer. 4. You must still be in transit / on the journey until the takbiratul ihram of the second prayer. 5. Trust that the time of the earlier prayer (Dhuhr or Maghrib) is still valid until the second prayer ('Asr or Isha') is performed.

Rules for Jama' Ta'khir

1. The niyyat (expression of intent) to jama' (combine) must be made during the prayer time of the earlier prayer, namely Dhuhr or Maghrib. 2. You must still be in transit / on the journey until the salaam of the second prayer.

Niyyat for Jama' Taqdim Without Qasr

أصلي فرض الظهراربع ركعات مجموعا إليهالعصر اداءلله تعالى

(I am expressing niyyat to perform the four rakaats of fard Dhuhr combined with it the prayer of 'Asr, for Allah Taala.)

Niyyat for Jama' Taqdim With Qasr

أصلي فرض الظهرركعتين قصرامجموعا إليه العصر اداءلله تعالى

(I am expressing niyyat to perform fard Dhuhr shortened to two rakaats combined with it the prayer of 'Asr, for Allah Taala.)

Niyyat for Jama' Ta'khir Without Qasr

أصلي فرض الظهراربع ركعات مجموعا إلى العصر اداءلله تعالى

(I am expressing niyyat to perform the four rakaats of fard Dhuhr to be combined with the prayer of 'Asr, for Allah Taala.)

Niyyat for Jama' Ta'khir With Qasr

أصلي فرض الظهرركعتين قصرامجموعا إلى العصر اداء لله تعالى

(I am expressing niyyat to perform fard Dhuhr shortened to two rakaats to be combined with the prayer of 'Asr, for Allah Taala.)