I heard the Messenger of Allah ﷺ say, "Allah has guaranteed for the one who goes out in His path, motivated by nothing except faith in Me and striving in My cause, that He will admit him into Paradise by one of two means, either through being killed or by natural death, or He will return him to the dwelling from which he set out, having attained whatever reward or spoils of war he gained."
أخبرنا قتيبة قال حدثنا الليث عن سعيد عن عطاء بن ميناء مولى ابن أبي ذباب سمع
سمعت رسول الله ﷺ يقول انتدب الله عز وجل لمن يخرج في سبيله لا يخرجه إلا الإيمان بي والجهاد في سبيلي أنه ضامن حتى أدخله الجنة بأيهما كان إما بقتل أو وفاة أو أرده إلى مسكنه الذي خرج منه نال ما نال من أجر أو غنيمة
[Its chain of transmission is hasan] Ahmad narrated it (494/2) from the hadith of Layth bin Saad through this same route, and it is also found in Kubra, hadith no. 4331. Ibn Manda also narrated it in Kitab Iman (397/12, no. 238) from the hadith of Qutayba bin Saeed through this same route. Saeed here is the son of Abu Saeed Maqburi.