It is narrated from Hazrat Abu Darda (may Allah be pleased with him) that once the Noble Prophet (peace and blessings be upon him) said: "Shall I not tell you of the best deed in the sight of your Lord, which raises you to the highest ranks, which is better for you than spending gold and silver, and better than meeting your enemy in the battlefield so that you strike their necks and they strike your necks?" The companions (may Allah be pleased with them) asked, "O Messenger of Allah! What is that deed?" The Noble Prophet (peace and blessings be upon him) said: "The remembrance of Allah."
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 21702
Hadith Gradingحکم دارالسلام:رفعه لا يصح، والصحيح وقفه على ابي الدرداء، فقد اختلف فى رفعه ووقفه، وفي ارساله ووصله