Asr prayer
The period of Asr prayer begins approximately when the sun is halfway down from noon to sunset (various branches of Islam differ on the starting point; some say that it begins when the shadow of an object equals its actual length plus its shadow during noon, others say that the actual length must be doubled), following Zuhr prayer, and ends at sunset, when Maghrib prayer begins. Shia Muslims are allowed to perform Zuhr and Asr prayers one after another, so they may perform the Asr prayer before the actual period begins. Barring the Hanafi school, which forbids prayer combination, Sunni Muslims may only do this if they are traveling and incapable of performing the prayers separately. Amongst Sunnis, Salafis allow the combining of prayers for a wide range of reasons such as when various needs or difficulties arise (taking precedence from Hanbali and Shafiite schools). Some Salafis amongst Ahl-i-Hadith consider combining prayers for no reason to be permissible.