The Messenger of Allah ﷺ said, "Whoever stands guard for one day and one night in the path of Allah will receive a reward equal to fasting a month and praying through its nights. Whoever dies while stationed on guard will continue to receive that same reward, his sustenance will keep flowing to him, and he will be safe from the trial of the grave."
قال الحارث بن مسكين قراءة عليه وأنا أسمع عن ابن وهب أخبرني عبد الرحمن بن شريح عن عبد الكريم بن الحارث عن أبي عبيدة بن عقبة عن شرحبيل بن السمط
عن رسول الله ﷺ قال من رابط يوما وليلة في سبيل الله كان له كأجر صيام شهر وقيامه ومن مات مرابطا أجري له مثل ذلك من الأجر وأجري عليه الرزق وأمن من الفتان
Muslim narrated it in "The Book of Leadership," in the chapter on the merit of guarding the frontier for the sake of Allah, mighty and exalted, hadith no. 1913, from the hadith of Ibn Wahb through this same chain. It is also found in Kubra, hadith no. 4375.