Is it possible to have one truly original thought not based on past impression?

Hume’s empiricist philosophy states that our all our mental ideas (which can be simple or complex) are based on simple or complex impressions; that which we perceive through our senses, emotions and passions.

Do you think that it is possible to conjure up a truly original simple idea or combinations of original ideas that cannot in any way be traced back to experience of the external world? If you do think it is possible, please provide me with an example.

I do not believe it is possible, hence my question.