Purity: Doubt Regarding the Order of Wudu and an Invalidator
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 301:
If someone knows he has performed wuḍūʾ and also knows that he has done something that invalidates wuḍūʾ – for example, he has urinated – but he does not know which one was first [i.e. he does not know whether he performed wuḍūʾ and then urinated, for example, or he urinated and then performed wuḍūʾ], then in the event that he has this doubt before prayers, he must perform wuḍūʾ for those prayers. If he has this doubt during prayers, he must break his prayer and perform wuḍūʾ. And if he has this doubt after prayers, the prayer he performed is valid but he must perform wuḍūʾ for subsequent prayers.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)