“Skill in action is called yoga.” This means that the same action, when it is done ordinarily, becomes the source of bondage; and when this action is done in the proper spirit, it purifies the mind and eventually destroys bondage. Thus it becomes yoga. For instance, work done with attachment leads to bondage; and when the same work is done with non-attachment, it becomes the cause of liberation. This attitude of attachment springs from yoga. Therefore, this very skill is called yoga.
(p. 194, Spiritual Treasures, Swami Turiyananda’s letter to Phani dt 6th January 1919)