Prophet greater than Baha'u'llah only after the passing of 500,000 years

"There is no record in history, or in the teachings, of a Prophet similar in station to Bahá'u'lláh having lived 500,000 years ago. There will, however, be one similar to Him in greatness after the lapse of 500,000 years…."

(From a letter written on behalf of Shoghi Effendi to an individual believer, December 24, 1941)
https://bahai-library.com/hornby_lights_guidance_2&chapter=4