What does the Hadith below mean? :
Narrated Fadalah ibn Ubayd:
The Prophet (ﷺ) said: Everyone who dies will have fully complete his action, except one who is on the frontier (in Allah's path), for his deeds will be made to go on increasing till the Day of Resurrection, and he will be safe from the trial in the grave. (Sunan Abi Dawud 2500)
Who are those that are on the frontier? What does it mean that their deeds will continuously increase?
Does it refer to the Prophets and the martyrs? Righteous deeds like praying and doing dhikr are still being performed by them even after they have died. Likewise, the deeds of the Prophets are continuously increasing because of the teachings and commandments that they brought as per the Hadith here. Is this interpretation correct?