Sunan an-Nasa'i 3167

It was narrated from Salman Al-Khair that the Messenger of Allah (ﷺ) said: “Whoever guards Ribat (the frontier) for one day and one night, will be given a reward like that for fasting and praying Qiyam for a month, and whoever dies at Ribat (guarding the frontier) will be rewarded, and he will be given provision, and he will be kept safe from Al-Fattan.” [1]
[1] According to As-Sindi, the preferred pronunciation is Al-Fattan, plural of Fatan refering to Al-Munkar and An-Nakir, while Al-Fattan would refer to Ash-Shaitan or the like, among the punishment of the grave, or, the angels of chastisement.