The Buddha on Equanimity

As a solid mass of rock
Is not stirred by the wind,
So a sage is not moved
By praise or blame.
As a deep lake
Is clear and undisturbed,
So a sage becomes clear
Upon hearing the Dharma.
Virtuous people always let go,
They don’t prattle about pleasures and desires.
Touched by happiness and then by suffering,
The sage shows no sign of being elated or depressed.

- Dhammapada


Equanimity is characterized as promoting neutrality toward all beings.
Its function is to see equality in beings. It is manifested as the quieting
of resentment and approval. Its proximate cause is seeing ownership
of deeds (karma) thus: “Beings are owners of their deeds.
Whose (if not theirs) is the choice by which they will become happy,
or will get free from suffering, or will not fall away from the success
they have reached?” It succeeds when it makes resentment and approval
subside, and if fails when it produces the equanimity of unknowing.

- Visuddhimagga 9.96


Rahula, develop meditation that is like the earth, for then agreeable
and disagreeable sensory impressions will not take charge of your
mind. Just as when people throw what is clean and unclean on the
earth – feces, urine, saliva, pus, or blood – the earth is not horrified,
humiliated, or disgusted by it; in the same way, agreeable and
disagreeable sensory impressions will not take charge of your mind
when you develop meditation like the earth..

- Majjhima-nikaya 62