One of the questions I get most told, is why the Shiites, merge / combine their prayers together. People have the misconception that it means that the Shias have only three prayers, but it does not. Shiites as Sunnis have evidence that it is alright to pray three times a day, and then merge Dhuhr and ASR and the Maghreb, and Isha.
"Prayer when the sun begins to drop until the darkness of the night, and [perform] the dawn prayer with reading [of the Koran]; reading at daybreak done in front of witnesses. "
(Qur'an: Chapter 17, Verse 78)
Why combine Shia Muslims prayers?
Shia Muslims acknowledge the five obligatory daily prayers. But often combine Zuhr and 'Asr prayers by performing them consecutively during the time period: start of Zuhr and the end of' Asr. They also consider it permissible to combine the Maghrib and 'Isha prayers in a similar manner. This practice is in complete agreement with the Qur'an as well as authentic traditions from the Prophet (S).
The Sunni legal schools (fiqh) - with the exception of the Hanafi school - allow the combination of the obligatory prayers (al-jam 'bayn al-salatayn) in case of rain, travel, fear, or other emergencies. In the Hanafi law school, it is forbidden to combine the daily prayers at any time, with the exception of the prayers at Al-Muzdalifa and during the Hajj. The Maliki, Shafi'i and Hanbali law schools all agree on the permissibility of combining the prayers when one is traveling, but have differences of opinion on other reasons. Ja'fari shi'iterna states that one can combine the prayers without any particular reason.
Prayer times in the Quran