I heard the Messenger of Allah ﷺ say, "By the One in whose hand is my soul, were it not that some men from among the believers cannot bear to stay behind from me, and I do not have the means to provide them with mounts, I would never stay behind from any expedition setting out to fight in the cause of Allah . By the One in whose hand is my soul, I would love to be killed in the cause of Allah, then brought back to life, then killed, then brought back to life, then killed, then brought back to life, then killed."
أخبرنا أحمد بن يحيى بن الوزير بن سليمان عن ابن عفير عن الليث عن ابن مسافر عن ابن شهاب عن أبي سلمة بن عبد الرحمن وسعيد بن المسيب أن
سمعت رسول الله ﷺ يقول والذي نفسي بيده لولا أن رجالا من المؤمنين لا تطيب أنفسهم أن يتخلفوا عني ولا أجد ما أحملهم عليه ما تخلفت عن سرية تغزو في سبيل الله عز وجل والذي نفسي بيده لوددت أني أقتل في سبيل الله ثم أحيا ثم أقتل ثم أحيا ثم أقتل ثم أحيا ثم أقتل
Bukhari narrated it in the Book of Wishing, in the chapter on what has been said about wishing and about the one who wishes for martyrdom, Hadith 7226, from the hadith of Layth bin Saad through him, and it is also in Al-Kubra, Hadith 4306.