For all thoughts the source is the 'I' thought. The mind will merge only by Self-enquiry 'Who am I?' The thought 'Who am l?' will destroy all other thoughts and finally kill itself also. If other thoughts arise, without trying to complete them, one must enquire to whom did this thought arise. What does it matter how many thoughts arise? As each thought arises one must be watchful and ask to whom is this thought occurring. The answer will be 'to me'. If you enquire 'Who am I?' the mind will return to its source (or where it issued from). The thought which arose will also submerge. As you practise like this more and more, the power of the mind to remain as its source is increased.
~Sri Bhagavan Ramana Maharishi