ANSWER:

This is not permissible and the prayer would be invalid if done intentionally 

You must wear an outer garment over such clothes that covers the entire body, bone structure and curves and a loose abaya would do the job perfectly 

QUESTION: If I am wearing a half sleeve shirt (kameez) and I wear a big scarf on it that covers upto my trunk during prayer, is my prayer valid? Because if I raise my hands for Takbeer the scarf also raises with it and someone in the front can see my hands uncovered.