Shafaqna (International Shia News Agency) – The Grand Ayatollah Sistani answered some questions regarding combining prayers.According to Shafaqna the question and answer are as follows:
Question: Why do Shias combine their prayers? Is it permissible to do so?
Answer: It is permissible to combine Zuhr and Asr prayers and to perform them separately as it is permissible in both manners. It is narrated that the Holy Prophet of Islam (pbuh) offered his prayers in both combined as well separate manners. He combined his prayers without being in an urgent situation like war or storm.
Source: Ayatollah Sistani