Is it permissible to prolong prostration after intending to rise from it, or to move slightly in preparation for rising?

If a worshiper moves slightly to rise from prostration (sujud) and then wishes to increase their prostration, there is no issue, especially if they did not actually move but only intended to in their mind. Shifting slightly does not invalidate the prayer, nor does it require a prostration of forgetfulness (sujud al-sahw).