I heard the Messenger of Allah ﷺ say: Keeping watch for a day and a night is better (in point of reward) than fasting for a whole month and standing in prayer every night. If a person dies (while, performing this duty), his (meritorious) activity will continue and he will go on receiving his reward for it perpetually and will be saved from the torture of the grave.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ رِبَاطُ يَوْمٍ وَلَيْلَةٍ خَيْرٌ مِنْ صِيَامِ شَهْرٍ وَقِيَامِهِ وَإِنْ مَاتَ جَرَى عَلَيْهِ عَمَلُهُ الَّذِي كَانَ يَعْمَلُهُ وَأُجْرِيَ عَلَيْهِ رِزْقُهُ وَأَمِنَ الْفَتَّانَ  

This tradition has been handed down on the authority of Salman al-Khair through another chain of transmitters.  

عَنْ رَسُولِ اللَّهِ ﷺ بِمَعْنَى حَدِيثِ اللَّيْثِ عَنْ أَيُّوبَ بْنِ مُوسَى