Sri Aurobindo
Letters of Sri Aurobindo
Volume II - Part 2
It is of course because of the old habit of the mental consciousness that it goes on receiving the thoughts from outside in spite of its being a fatigue – not that it wants them, but that they 
are accustomed to come and the mind mechanically lets them in and attends to them by force of habit. This is always one of the chief difficulties in Yoga when the experiences have begun and the mind wants to be always either concentrated or quiet. Some do what you propose [direct rejection of thoughts] and after a time succeed in quieting the mind altogether or the silence comes down from above and does it. But often when one tries this, the thoughts become very active and resist the silencing process and that is very troublesome. Therefore many prefer to go on slowly letting the mind quiet down little by little, the quietness spreading and remaining for longer periods until the unwanted thoughts fall away or recede and the mind is left free for knowledge from within and above.
What you might do is to try and see what results – if the thoughts attack too much and trouble, you could stop – if the mind quiets down quickly or more and more, then continue.