Rasulullah (sallallaho alaihe wasallam) once said to his companions,

"Shall I tell you something that is the best of all deeds, constitutes the best
act of piety in the eyes of your Lord, will elevate your status in the Hereafter,
and carries more virtue than the spending of gold and silver in the service of
Allah or taking part in JIHAD and slaying or being slain in the path of Allah?"
The Companions said, "Yes, O Messenger of Allah!"
The Prophet (Sallallaho alaihe wasallam) replied,

"It is the Zikr of Almighty Allah."


(Narrated by Tirmidhi, Ahmad, and Hakim who declared its chain of narrators sound )