It wasnarrated from Abu Hurairah that the Messenger of Allah (ﷺ)said:
"Allah has prepared (reward) for those who go out (to fight) inHiscause: 'And do not go out except (to fight) for Jihad in My cause,out of faith in Me and belief in My Messengers, but he has aguaranteefrom Me that I will admit him to Paradise, or I will returnhim to hisdwelling from which he set out, with the reward that heattained, orthe spoils that he acquired.' Then he said: 'By theOne in Whose Handis my soul, were it not that it would be toodifficult for theMuslims, I would never have stayed behind from anyexpedition thatwent out in the cause of Allah. But I could not findthe resources togive them mounts and they could not find theresources to follow me,nor would they be pleased to stay behind if Iwent. By the One inWhose Hand is the soul of Muhammad, I wish Icould fight in the causeof Allah and be killed, then fight and bekilled, then fight and bekilled.'"
English reference: Vol. 4, Book 24, Hadith 2753
Arabic reference: Book 24, Hadith 2858