Why Do We Pray Five Prayers In Three Times?

What is the reason that we pray Zuhr-Asr and Maghrib-Isha prayers together, whereas for every Prayer there is a special time and the great leaders of Islam used to pray on the particular times. That is they used to pray five prayers are five different times a day?
Answer: There is no scope of argument in this matter that to establish Prayers five times a day and pray on the special times had been the practice of the Holy Prophet (s.a.w.a.), the holy Imam (a.s.) and the common Muslims at the early period of Islam and they used to generally pray five prayers at five different times.