The Rudiments of Wudu'

 Allah, the Exalted, says, (translated),
"O you who believe!  When you stand for prayer, then wash your faces, and your hands upto the elbows, and wipe your heads, and [wash] your feet upto the ankles."

So, the obligatory elements of purification [i.e. wudu'] are:  Washing the three parts [the face, the two arms, and the two feet].  The elbows and the ankles are included in washing. Wiping the head - the obligatory [part] in wiping the head is the extent of the forelock [one-fourth], based on that which
Mughirah ibn Shu`bah narrated, that the Prophet (may Allah bless him and grant him peace) made wudu' and wiped his forelock and his khuffs.