Abu Hurairah reported,
The Prophet ﷺ said, "Allah 
has guaranteed to protect the person who goes out in His path, driven by nothing except striving in the cause of Allah and belief in His words, until He either grants him entry into Paradise or returns him to his home from which he set out."
Ahmad 9174
Sahihحدثنا معاوية بن عمرو قال حدثنا زائدة قال حدثنا أبو الزناد عن عبد الرحمن الأعرج
عن أبي هريرة
عن النبي ﷺ قال توكل الله عز وجل بحفظ امرئ خرج في سبيل الله لا يخرجه إلا الجهاد في سبيل الله وتصديق بكلمات الله حتى يوجب له الجنة أو يرجعه إلى بيته أو من حيث خرج
No references are available.
Its chain of transmission is sahih. Bukhari reported it, 19/4, in the Book of Jihad, chapter "The best of people is a believer who strives with himself," and Nasai reported it, 16/6, number 3122, in the Book of Jihad, chapter "What Allah has guaranteed for one who strives in His cause."