Musnad Abu Ya'la al-Mawsili 160:207

And with his chain of narration from Abu Hurairah, he said: A man came to the Messenger of Allah, may Allah bless him and grant him peace, and said: "O Messenger of Allah, he who fights in the way of Allah, does he enter Paradise?" He said: "Yes." Then he remained silent for a short while, as if he had heard something, and said: "Where is the questioner from just now?" The man stood up and said: "What did you say?" He said: "I said: Have you considered he who strives in the way of Allah and is killed, does he enter Paradise? I said: Yes." He said: Then he said: "Indeed, Gabriel has informed me of that, unless he has a debt upon him."