When other thoughts arise, one should not pursue them,
but should inquire: 'To whom do they arise?' It does not
matter how many thoughts arise. As each thought arises,
one should inquire with diligence, "To whom has this
thought arisen?". The answer that would emerge would be
"To me". Thereupon if one inquires "Who am I?", the mind
will go back to its source; and the thought that arose
will become quiescent.

With repeated practice in this manner, the mind will
develop the skill to stay in its source. When the
mind that is subtle goes out through the brain and the
sense-organs, the gross names and forms appear; when it
stays in the heart, the names and forms disappear. Not
letting the mind go out, but retaining it in the Heart is
what is called "inwardness" (antar-mukha). Letting the
mind go out of the Heart is known as "externalisation"
(bahir-mukha). Thus, when the mind stays in the Heart,
the 'I' which is the source of all thoughts will go, and
the Self which ever exists will shine. Whatever one does,
one should do without the egoity "I". If one acts in that
way, all will appear as of the nature of Siva (God).

                        - Ramana Maharshi