The completion (or perfection) of ablution (one should wash all the parts perfectly)

Narrated Usama bin Zaid:

Allah's Messenger (ﷺ) proceeded from `Arafat till when he reached the mountain pass, he dismounted, urinated and then performed ablution but not a perfect one. I said to him, ("Is it the time for) the prayer, O Allah's Messenger (ﷺ)?" He said, "The (place of) prayer is ahead of you." He rode till when he reached Al-Muzdalifa, he dismounted and performed ablution and a perfect one, The (call for) Iqama was pronounced and he led the Maghrib prayer. Then everybody made his camel kneel down at its place. Then the Iqama was pronounced for the `Isha' prayer which the Prophet (ﷺ) led and no prayer was offered in between the two . prayers (`Isha' and Maghrib).