Riyad us Saliheen: Hadith 1291

The Messenger of Allah (ﷺ) said, "The actions of every dead person come to a halt with his death except the one who is on the frontier in Allah's way (i.e., observing Ribat). This latter's deeds will be made to go on increasing for him till the Day of Resurrection, and he will be secure from the trials in the grave."

[Abu Dawud and At- Tirmidhi].