Allah Subhanah wa a'ala states in the Qur'an that for every people, He has commanded to perform religious rituals and for the people of the Prophet Muhammad, one of the rituals of worship is the obligatory prayer five times a day as is done and taught by the Prophet.
Worshiping God as our Creator God, is very broadly implicated. Worship means worshiping, serving and obeying God in our whole life. We are born as servants of Allah SWT, we can not give up in serving and obeying Him at any time or under any circumstances. Just as we can not say that we are God's servants for a certain time, we can not say that we will spend only a certain time in worshiping Him, and spend the rest of the time for something else. He created us to worship Him, and we have the duty, the duty and the responsibility that our whole life will be dedicated to worship Him. 