How authentic are the hadiths that mention that whoever dies stationed in the path of Allah will be safe from the trial of the grave?

Whoever dies while on ribat (guard duty) in the path of Allah will be safe from the trial of the grave. He will not be asked the well-known questions, and his ribat will testify to his truthfulness. A murabit (one on ribat) is he who stations himself at the frontiers where enemy attacks are feared. The proof of his virtue is the hadith of Salman, may Allah be pleased with him: "Guard duty for a day and a night is better than fasting for a month and praying during its nights. And if he dies, his deeds that he used to do will continue to be recorded for him, his provision will continue to be given to him, and he will be safe from the Fattan (the trial of the grave)." And the hadith of Fadalah ibn Ubaid, may Allah be pleased with him: "Every dead person's deeds are sealed, except for the one who dies on ribat in the path of Allah, for his deeds will continue to grow until the Day of Resurrection, and he will be safe from the trial of the grave." The meaning of his safety from the Fattan or the two Fattan of the grave (Munkar and Nakir) is that they will not come to him or test him. Rather, his death while on ribat is sufficient as proof of the soundness of his faith.