A sahabi once said,
"O Rasulullah (Sallallaho alaihe wasallam),
I know that the commandments of Shariat are many,
but of these tell me the one that I may practice
assiduously throughout my life."
The Prophet (Sallallaho alaihe wasallam), replied,
"Keep your tongue always moist (i.e. busy) with the 'Dhikr' of Allah".
{ Tirmidhi, Ibn Majah }
