Musnad Ahmad 788:54

Bahz narrated to us, Ja'far ibn Sulayman narrated to us, Abu 'Imran al-Jawni narrated to us, from Abu Bakr ibn 'Abd Allah ibn Qays, who said: I heard my father, while he was in the presence of the enemy, saying: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "Indeed, the gates of Paradise are under the shadows of the swords." He said: Then a man from the people, disheveled in appearance, stood up and 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 said: So he returned to his companions and said: "I bid you peace." Then he broke the scabbard of his sword and threw it away, then walked with his sword and struck with it until he was killed.