:salam2:
On the Day of Resurrection, some followers of the Prophet Muhammad 
will be called as “Al-Ghurr-ul-Muhajjalun”. My question is:
1- What is the meaning of “Al-Ghurr-ul-Muhajjalun”
2- Why ‘they’ will be called by this?
Please share you knowledge/info related to this 
Re: Al-Ghurr-ul-Muhajjalun
Peace,
**Book ‘Ablutions (Wudu)’ of Sahih Bukhari, Hadith No. 138. **
Narrated Nu’am Al-Mujmir: Once I went up the roof of the Masjid, 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).’ "
Re: Al-Ghurr-ul-Muhajjalun
Peace,
Al-Ghurr'a have many meanings. Here in hadith it is stated towards a beauty or shinny. Like a horse having a white surface on his face which increase in his beauty.
It also means something that glue with it i.e., stick on or overcome on something. Also referred as water overcomes to fire.
**Muhajjalun **referred to the whitening or shinning of one out of three from a sea-horse.