Riyad us Saliheen: Hadith 1440

The Messenger of Allah (ﷺ) said, "Shall I not inform you of the best of your actions which are the purest to your Rubb, which exalt you to the high ranks, which are more efficacious than spending gold and silver (in charity), and better for you than you should encounter your enemies whom you will smite their necks and they will smite your necks?" They said, "Certainly." He (ﷺ) said, "Remembrance of Allah the Exalted."

[At-Tirmidhi].