Dhikr

Abu al-Darda narrates: The Prophet ﷺ once asked his Companions: “Shall I tell you about the best of Allah deeds, the best act of piety in the eyes of your Lord, which 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 Dhikr of Allāh.”
— Related by Malik, Ahmad & others.