Narrated Jabir ibn Abdullah: The Messenger of Allah ﷺ stayed at Tabuk twenty days; he shortened the prayer (during his stay). Abu Dawud said: No one narrates this tradition with continuous chain except Mamar.
Explanation & Benefits
Shaykh Umar Farooq Saeedi
1235. Commentary:
When the mujahideen are at the borders in a state of war or there is a danger of war, they should perform shortened (qasr) prayers... no matter how long this period lasts. However, when there is neither a state of war at the borders nor any fear of war from the enemies, then it is not correct for the stationed soldiers and mujahideen at the border to continue performing shortened (qasr) prayers permanently.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 1235