Hadithcore
Mishkat al-Masabih, 3789

He reported God’s Messenger as saying, “God answers the prayer for forgiveness of him who goes out in His path, being led to do so by nothing but faith in Him and belief in His Messengers, promising to bring him back with the reward or booty he obtains, or bring him into paradise.” (Bukhari and Muslim.)

وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «انْتَدَبَ اللَّهُ لِمَنْ خَرَجَ فِي سَبِيلِهِ لَا يُخْرِجُهُ إِلَّا إِيمَانٌ بِي وَتَصْدِيقٌ بِرُسُلِي أَنْ أَرْجِعَهُ بِمَا نَالَ مِنْ أَجْرٍ وَغَنِيمَةٍ أَوْ أُدْخِلَهُ الْجَنَّةَ»

References1 variant
In-Book Reference
Book 19, Hadith 3