Surah At-Taubah, Ayat 43-44

Ayat 43. May Allah forgive you. Why did you grant them leave (for remaining behind, you should have persisted as regards your order to them to proceed on Jihad), until those who told the truth were seen by you in a clear light, and you had known the liars?
Ayat 44. Those who believe in Allah and the Last Day would not ask your leave to be exempted from fighting with their properties and their lives, and Allah is the All-Knower of Al-Muttaqun (the pious).

Hazrat Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah [SAWW](PBUH) said, "In Jannah there are a hundred grades which Allah has prepared for those who fight in His Cause; and the distance between any two of those grades is like the distance between the heaven and the earth.''[Al-Bukhari Hadith # 2790].

Lesson : as mentioned above in Surah At-Taubah Ayat 44. "Those who believe in Allah and the Last Day would not ask your leave to be exempted from fighting with their properties and their lives", This Hadith also tells us about the distinction of Mujahid who love to fight for the cause of Allah (SWT) and in the Hereafter and their elevation to high position.