Thank you dear Dr. Izadi .
We have this discussion in our Arabic Ahl A; Quran section.
If making Voozoo is a starting part of each prayer and not separated from praying, it will no need to mention what invalidates it ( Going to bath room , having sexual intercourse ).
By one Voozoo you can pray more than one prayer if you keep yourself without going to bathroom and sexual enter course.
Actually, the Islamic religion is based on convenience : (God doth not wish to place you in a difficulty, ) 5 : 6 ) ( He has chosen you, and has imposed no difficulties on you in religion ) ( 22 : 78 )( - God doth wish to lighten your (difficulties): for man was created weak (in flesh). )4 : : 28 )