Washing all the limbs in wudhu one time

The fardh wudhu will be done, however one will not receive the reward of practicing on the sunnah. The sunnah is that one washes each limb thrice. The fuqaha have ruled that if one makes a habit of leaving out the sunnah (e.g. one washes the limbs in wudhu once, not thrice), then one will become sinful.

And Allah Ta'ala (الله تعالى) knows best.