The Essential Foundation for 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 and 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):
https://What-Buddha-Said.net/drops/What_is_Right_Awareness.htm
https://What-Buddha-Said.net/drops/III/Awareness_Sati.htm
https://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..