Volume 1, Book 4, Number 138 :
Narrated by Nu'am Al-Mujmir
Once I went up the roof of the mosque, along with Abu
Huraira. He perform ablution and said, "I heard the
Prophet saying, "On the Day of Resurrection, my followers
will be called "Al-Ghurr-ul-Muhajjalun" from the trace of
ablution and whoever can increase the area of his
radiance should do so (i.e. by performing ablution
regularly).' "