Musnad Ahmad 1118:17

And with this chain of narration, from Fudalah ibn Ubayd, he said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Every dead person has his deeds sealed, except for the one who died stationed (as a Murabit) in the way of Allah; for his deeds will continue to grow until the Day of Resurrection, and he will be secure from the trial of the grave." He said: And I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "The Mujahid (struggler) is the one who struggles against his own self for the sake of Allah," or he said: "in Allah."