Sahl bin Sa'd (May Allah be pleased with him) reported

The Messenger of Allah (ﷺ) said, "Observing Ribat (e.g., guarding the Islamic frontier for the sake of Allah) for a single day is far better than the world and all that it contains. A place in Jannah as small as the whip of your horse is far better than the world and all that it contains. An endeavour (fighting) in the Cause of Allah in the evening or in the morning is far better than the world and all that it contains."

[Al-Bukhari and Muslim].