Cleanliness (Taharah) is an important precondition of Islamic worship.
Wudu is an essential part of Cleanliness. Salah(prayer) is not valid without
Wudu' or Tayammum(dry Ablution). Allah says in the Qur'an :
"Surely Allah loves those who turn to Him and those
who care for cleanliness" (2:22).
At the end of the above steps recite:
"Ash-hadu an la ilaha illal lahu wa ash-hadu anna Muammadan 'abduhu
Meaning: I testify that there is no god but Allah and He is One and
has no partner and I also testify that Muhammad is His servant and messenger.
You Should repeat your Wudu after :
1. Natural discharge (e.g. urine, stool, wind and the like)
2. Flow of blood or pus from any part of the body.
3. Full mouth vomiting
4. Falling asleep.