Abu Hurayra raa narrated that the Messenger of Allah pbuh said: “On the Day of Resurrection, my followers will be called Al-Ghurrul-Muhajjalun from the trace of ablution”.
Ghurr in arabic means the bright radiance that is on the forehead of a horse. It is used here to represent beauty and fame. In this hadith, it means the light that will radiate on the face of the followers of Muhammad pbuh.
Muhajjal means the whiteness that is on the feet of a horse. The two words are meant to indicate light that will illuminate from their faces and limbs. May Allah include us amongst them. Ameen summa ameen.
The Messenger of Allah pbuh went to the (Baqi`) cemetery and said, “May you be secured from punishment, O dwellers of abode of the believers! We, if Allah wills, will follow you. I wish we see my brothers.” The Companions said, “O Messenger of Allah! Are not we your brothers?” He pbuh said, “You are my Companions, but my brothers are those who have not come into the world yet.” They said; “O Messenger of Allah! How will you recognize those of your Ummah who are not born yet?” He pbuh said, “Say, if a man has white-footed horses with white foreheads among horses which are pure black, will he not recognize his own horses?” They said; “Certainly, O Messenger of Allah!” He pbuh said, “They (my followers) will come with bright faces and white limbs because of wudu ; and I will arrive at the Hawd (Al-Kauthar) ahead of them.” Muslim
-Encyclopedia of Islamic Jurisprudence- Darussalam, Muslim Matters.