Sunan Ibn Majah — The Chapters on Jihad — Hadith No: 2753
Translation
It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:“Allah has prepared (reward) for those who go out (to fight) in His cause: ‘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 a guarantee from Me that I will admit him to Paradise, or I will return him to his dwelling from which he set out, with the reward that he attained, or the spoils that he acquired.’ Then he said: ‘By the One in Whose Hand is my soul, were it not that it would be too difficult for the Muslims, I would never have stayed behind from any expedition that went out in the cause of Allah. But I could not find the resources to give them mounts and they could not find the resources to follow me, nor would they be pleased to stay behind if I went. By the One in Whose Hand is the soul of Muhammad, I wish I could fight in the cause of Allah and be killed, then fight and be killed, then fight and be killed.’”