The Final Word:
Clement of Alexandria
Theologian of Athens, Greece and Alexandria, Egypt (200-258 AD)

As for times of prayer, nothing at all has been prescribed except clearly to “pray at every time and every place.” However, the outward observance of certain hours will not be unprofitable. I mean those common hours that mark the intervals of the day—the third, the sixth, and the ninth—which we may find in the Scriptures to have been more solemn than the rest.
Just as we read this to have been observed by Daniel, we also pray at a minimum of not less than three times during the day; for we are debtors to Three: Father, Son, and Holy Spirit. Of course, in addition to our regular prayers that are due without any admonition, we should pray at the entrance of light and of night. Furthermore, it is becoming for believers not to take food nor go to the bath before interposing a prayer. For the refreshments and nourishments of one’s spirit are to be held prior to those of one’s flesh.
In Luke’s writings, the third hour is demonstrated as an hour of prayer. It was about this hour that those who had received the inaugural gift of the Holy Spirit were thought to be drunkards. And then there is the sixth hour, at which hour Peter went up on the roof. Finally, there is the ninth hour, at which hour they entered the Temple. Why should we not understand that, with absolute perfect indifference, we must pray always, everywhere, and at every time. Still, these three hours are distinguished in human affairs. For they divide the day, distinguish business, and reverberate in the public ear. They have likewise always been of special solemnity in divine prayers. Again, this is a prac-tice that is sanctioned also by the corroborating fact that Daniel prayed three times each day.
“In time we’ll find that our prayers