The dream is witnessed without the physical eyes, so it was not the waking entity, which witnessed the dream

Those that want to prove existence of formless witness; it is only in its presence, for it is awareness, that proof can be given. It is a pre-condition without which one cannot talk of proof.  The formless witness is the substance and witness of the waking experience, which contains man, and his experience of the world.  Without the waking experience man and his experience are absent. The three states are transient in nature.  Thus there must be a knower of the three states which appear and disappear in succession.

 Only through deeper analysis the three states, one becomes aware of the formless witness. 

v  How does one see the dream?

The dream is witnessed without the physical eyes, so it was not the waking entity, which witnessed the dream. The waking entity and the waking world was absent in the dream. If the dream world were without the witness, it is impossible to witness the dream. Therefore there must be a witness of the dream. This same witness is witnesses the waking experience as a whole. And also the deep sleep.  Thus the formless witness has to be mentally grasped by constant reflecting on the subject.

The gross waking experience is merged into the mental experience in the sense that when it is analyzed, it is found to exist inseparably in and as the mind alone.  All "spiritual" planes are really mental.

The existence of the three states is the proof of the Formless witness. The moment one becomes aware of the witness of the dream is not the waking entity, then he becomes aware of the formless witness of the three states, which is apart from the three states.