Musnad Abu Ya'la al-Mawsili 243:109

Ibrahim ibn Abdullah al-Harawi narrated to us, Ja'far narrated to us, from Abu 'Imran, from Abu Bakr ibn Abi Musa, who said: I heard Abu Musa saying: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "The gates of Paradise are under the shadows of the swords." A man with a disheveled appearance said, "O Abu Musa, did you hear this from the Messenger of Allah (peace and blessings of Allah be upon him)?" He said, "Yes." He then went to his companions and said, "I bid you peace." Then he broke the scabbard of his sword, threw it toward the enemy, and fought with it until he was killed.