Abdullah bin Umar reported,
The Prophet ﷺ narrated, relating from his Lord 
, that He said, "Any servant of Mine who goes out as a warrior in My path, seeking My pleasure, I guarantee that I will return him with whatever reward and spoils he has gained, and if I take his soul, I will forgive him, have mercy on him, and admit him to Paradise."
Ahmad 5977
Sahihحدثنا روح حدثنا حماد بن سلمة عن يونس عن الحسن
عن ابن عمر
عن النبي ﷺ فيما يحكي عن ربه تبارك وتعالى قال أيما عبد من عبادي خرج مجاهدا في سبيلي ابتغاء مرضاتي ضمنت له أن أرجعه بما أصاب من أجر وغنيمة وإن قبضته أن أغفر له وأرحمه وأدخله الجنة
Its isnad is sahih. Yunus is Ibn Ubayd. Al-Hasan is al-Basri. The hadith was reported by Nasai (2:57) through Hammad bin Salama, with this isnad. Munziri mentioned it in Targhib wal-Tarhib (2:166) and attributed it to Nasai alone. Suyuti mentioned it in Jami Saghir (6040) and attributed it to Ahmad and Nasai, marking it with the symbol for sahih. Munawi mentioned it in Ahadith Qudsiyyah, number 40, and attributed it to both of them and to Tabarani in al-Kabir.As for his saying "of reward and spoils," this is what is established in the three original manuscripts of the Musnad and in the book Ahadith Qudsiyyah, while in Nasai, Targhib wal-Tarhib, and Jami Saghir it reads "of reward or spoils."