Reference: http://www.alfawzan.af.org.sa/node/16637
Question: When praying, some people do not do so with complete submission and humility, so does this [in any way] reduce their reward?
Response: And how does he know that about them?! [The matter of praying with] complete submission and humility is something between the worshipper and his Lord, [so] how does he know [such-and-such] is not [praying with] complete submission and humility?
[That said] however, [know that] complete submission and humility is the soul and essence of the prayer, and so the Muslim is required to pray with complete submission and humility, [as Allaah (‘Azza wa Jall) says]: