It was narrated from Ibn 'Umar, from the Prophet (ﷺ), of what he related from his Lord, the Mighty and Sublime: "And of My slaves who goes out as a Mujahid striving in the cause of Allah, seeking my pleasure, I guarantee that I will bring him back with whatever he had earned as reward or spoils of war, and if I take his (soul) I will forgive him and have mercy on him."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنِي إِبْرَاهِيمُ بْنُ يَعْقُوبَ، قَالَ حَدَّثَنَا حَجَّاجٌ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ يُونُسَ، عَنِ الْحَسَنِ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم فِيمَا يَحْكِيهِ عَنْ رَبِّهِ عَزَّ وَجَلَّ قَالَ " أَيُّمَا عَبْدٍ مِنْ عِبَادِي خَرَجَ مُجَاهِدًا فِي سَبِيلِ اللَّهِ ابْتِغَاءَ مَرْضَاتِي ضَمِنْتُ لَهُ أَنْ أَرْجَعَهُ إِنْ أَرْجَعْتُهُ بِمَا أَصَابَ مِنْ أَجْرٍ أَوْ غَنِيمَةٍ وَإِنْ قَبَضْتُهُ غَفَرْتُ لَهُ وَرَحِمْتُهُ " .
sunnah.com