The ornament of the believer will reach as far as his ablution reaches

The Prophet (may Allah's peace and blessings be upon him) gives his followers the glad tidings that Allah, Glorified and Exalted, will grant them a sign of virtue and honor on the Day of Resurrection that will distinguish them from other nations. When called out, they will emerge, distinct from the rest of people with their radiant faces, hands and feet. This light is from the traces of a great act of worship, i.e. ablution, which they often performed on their limbs.

In that they sought Allah's pleasure and reward, hence they will have admirable reward of illumination. Abu Hurayrah recommended to extend this radiance, because washing more space of the body yields more radiance. Indeed, the ornamentation of light reaches as far as the water of ablution reaches. However, in mandatory ablution, one washes the hands up to the elbow and a little bit further, and washes the feet up to the ankles and a little bit further.

It is not required to wash the upper arms and shins.