All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
  is His slave and Messenger.
The Hadeeth that you mentioned in the question was reported by Muslim and narrated by Abu Moosa al-Ash’ari 
  that the Prophet 
  said: “There would come people amongst the Muslims on the Day of Resurrection with as heavy sins as mountains, and Allah would forgive these sins for them and place them on the Jews and the Christians.”
Nonetheless, we have not come across a narration that shows this category of Muslims as to who they are exactly, whether they are the Mujahideen, the martyrs, the scholars, or the common Muslims; Allah knows best about them.
Allah Knows best.