If you have wudu‘ and any of the matters which invalidate wudu‘ takes place, you must not pray until you make a new wudu‘. Among the invalidators of wudu’ are:
- The emission of any substance from the eliminatory outlets, such as urine, defecation, or gas, except maniyy.
- Touching the penis or vagina, or the anus with the inside of the bare hand (the palm).
- Losing the mind or losing consciousness.
- Sleeping without having the buttocks firmly seated, such as sleeping on the stomach, back, and on the side.
- Skin to skin contact with a member of the opposite sex, who has reached an age where he or she is normally desired (these whom one is not allowed to marry in any circumstance, such as one’s parent, sibling, etc. are not included).
If one of these matters happens to you during prayer, you stop the actions of the prayer, perform wudu‘ and then start the prayer from the beginning.