Sayyiduna Salman al-Farisi (may Allah be pleased with him) passed by Ibn al-Simt while he was stationed guarding the frontier in the path of Allah, and said to him: Shall I not encourage you in the work you are engaged in? Then he said: The Messenger of Allah (peace and blessings be upon him) said: "Guarding the frontier for one day in the path of Allah is better than fasting a month and standing in prayer during it; and whoever dies while guarding the frontier in the path of Allah, his deed, or his deeds, will continue (to be recorded) for him, and he will be protected from the trial of the grave."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6052