Bhagavad Gita 4.18कर्मण्यकर्म यः पश्येदकर्मणि च कर्म यः।स बुद्धिमान् मनुष्येषु स युक्तः कृत्स्नकर्मकृत् ॥

In common parlance action means movement of the body, movement of the hands and feet, and inaction means to sit quiet.It is the idea of agency, the idea I am the doer that binds man to Samsara. If this idea vanishes, action is no action at all. It will not bind one to Samsara. This is inaction in action. If you stand as s spectator or silent witness of Natures activities, feeling Nature does everything I am nondoer (Akarta), if you identify yourself with the actionless Self, no matter what work or how much of it is done, action is no action at all. This is inaction in action. By such a practice and feeling, action loses its binding nature.A man may sit quietly. He may not do anything. But if he has the idea of agency or doership, or if he thinks that he is the doer, he is every doing action, though he is sitting quietly. This is action in inaction. The restless mind will ever be doing actions even though one sits quietly. Actions of the mind are real actions. Nor can anyone even for one moment remain really actionless, for helplessly is everyone driven to action by the alities of Nature. (Chapter III.5)Inaction also induces the feeling of egoism. The inactive man says, I sit quietly I do nothing. Inaction, like action, is wrongly attributed to the Self.He is the performer of all actions who knows this truth