The Essential Foundation of Mental Purity!

The Blessed Buddha once said:
Bhikkhus, there are these
Four Foundations of Awareness. What four?
When a Bhikkhu keenly contemplates:
1: Any
Body just as a transient
Form...
2: Any
Feeling just as a passing
Sensation...
3: Any
Mind just as a momentary
Mood...
4: Any
Phenomena just as a flickering
Mental State...
while always
acutely aware & clearly comprehending, he thereby removes
any urge, envy, jealousy, frustration and discontent rooted in this
world...
These are the
Four Foundations of Awareness...

Details On Foundations of Awareness (Sati):
http://What-Buddha-Said.net/drops/What_is_Right_Awareness.htm
http://What-Buddha-Said.net/drops/III/Awareness_Sati.htm
http://What-Buddha-Said.net/drops/III/Sati_Summary.htm

Source of reference (edited extract):
The Grouped Sayings of the Buddha.
Samyutta Nikāya.
Book [V: 173-4] 47 The Foundations of Awareness: 24 Simple..