The Messenger of Allah SAW (1) said: "Shall I not tell you the most in goodness of your deeds, the nicest to Your Owner, the highest in your ranks, better for you than spending gold and silver, and better for you than meeting your enemy whereupon you strike their necks and they strike your necks?" They said "Yes O' Messenger of Allah." He said: "Remembrance of Allah."
(1) is read as Salla 'allahu 'alayhi wassallam, and may be translated as "May Allah bestow his Grace, Honor, and Peace upon him."
Reported by At-Tirmithi, Al-Bukhari, Ibn Majah, and Al-Hakim who said it was of sound ascription (Saheeh Isnad). Al-Albani included this hadeeth in The Authentic of Good Sayings as #1.