Sunan an-Nasa'i 3151

It was narrated from Abu Hurairah that the Prophet (ﷺ) said:"Were it not that it would be too difficult for my Ummah, I would not have stayed behind from any expedition. But they could not find mounts, and I could not find any mounts for them, and it would be too hard for them to stay behind when I went out. And I wish that I could be killed in the cause of Allah, then brought back to life, then killed, then brought back to life, then killed," three times