One of the five pillars of Islam is prayer—done five times a day—and nothing must interfere with praying. The words spoken in prayer are the Moslem's tools for connecting with God and are paramount to one's existence. It's imperative, during the prayer, that one's mind doesn't drift off and entertain thoughts other than the words of the prayer itself.
One day a man went to his mufti and asked him: “Are tears allowed during prayer?”
“Depends on the tears, my good man,” replied the mufti.
“How so?”
“If the tears have their source in the spiritual world—if they've sprung forth because of a spiritual experience and one's established a connection with the divine—then tears are a grace! However, if they've sprung from some physical pain or emotional discomfort, then they're a distraction and indeed may cut off one's connection with God; such tears are certainly not welcome.”
The Moslem had his answer, thanked the mufti graciously, and left for the mosque.