In the Mi’raj fifty daily prayers were prescribed for the believers. However, their number was later reduced to five. This was done to impress upon man that he had been found capable by God of devoting such a large part of his time and energy to His worship. The one who keeps this in mind will never regard the five daily prayers as excessive. In fact, he will realize that he had been found worthy of much more and had the Lord, out of His Grace, not made the concession, he would be carrying out His command dutifully and performing as many as fifty prayers (salāh) every day. God showed his favor to him and made the five prayers equivalent of fifty in reward. However, the original command is there to stir his ambition and urge him on to greater effort.
From Abul Hasan Ali Nadwi (1913-1999), The Four Pillars of Islam, p. 11.
 Prophet Muhammad's Night Journey.