The Holy Prophet [s] said: "There is a goodness above any goodness until when a believing person, (fighting against the enemies of Islam who slaughter Muslims), is killed in the way of Allah, Almighty and Glorious, then there is no goodness above it."
Bihar-ul-Anwar, vol. 10, p. 100
Imam Sadiq [a] said: "He who is slain in the path of Allah (as a martyr), He will not recount anything of his sins to him, (his sins will be forgiven totally)."
Furu-I-Kafi, vol. 5, p. 54
The Holy Prophet [s] said: "...By the One in Whose hand is my soul, if all the members in the skies and on the earth gather to kill a (sinless) believer or be persuaded to it, Allah will surely put them all in the Fire."
Bihar-ul-Anwar, vol. 75, p. 149
The Holy Prophet [s] said: "No drop is more beloved with Allah, Almighty and Glorious, than the drop of blood which is poured in the way of Allah.
Wasa'il-ush Shi'ah, vol. 15, p. 14