I heard the Messenger of Allah ﷺ say, "Standing guard at the frontier for a day and a night is better than fasting and praying through an entire month. If he dies during it, the deeds he used to perform will continue to be credited to him, his provision will keep flowing to him, and he will be safe from the trial of the grave."
سمعت رسول الله ﷺ يقول: رباط يوم وليلة خير من صيام شهر وقيامه، وإن مات جرى عليه عمله الذي كان يعمله، وأجرى عليه رزقه، وأمن الفتان.
Muslim narrated it in the Book of Leadership (1913), from Abdullah bin Abdul-Rahman bin Bahram Darimi, who said, Abu Walid Tayalisi told us, who said, Layth (meaning Ibn Saad) told us, from Ayub bin Musa, from Makhul, from Shurahbil bin Simt, from Salman, and he mentioned it.His statement, "al-fattan," is with the fa pronounced with a u sound, the plural of fatin, and it is taken to refer to the various kinds of trial that come after burial, from the pressing of the grave, and the questioning and punishment in the grave. Some scholars vowel it with the fa pronounced with an a sound, meaning the one who tries the buried person through questioning and thereby punishes him.