Is it permissible for one who suffers from intrusive thoughts of disbelief (kufr) to take the least likely possibility and assert that he pronounced the Two Testimonies with certainty merely because there is a possibility in his mind that he did so?

The person afflicted with misgivings should disregard and pay no attention to the misgivings of disbelief; for indulging in them leads to great evil, and you are upon goodness as long as you strive against these misgivings. You are not required to utter the Two Testimonies because of these misgivings, and if you doubt whether you have done something (like reciting the Tashahhud) or not, then build upon the assumption that you have done it, and pay no attention to the misgivings.