Prophet Muhammed (salallaahu alaihi wasallam) has described Paradise to be a place, “No eye has seen, no ear has heard and neither has the thought occurred in any person’s heart.” [Bukhari]

Can you explain how then the Prophet (salallaahu alaihi wasallam) saw Paradise during the Night Journey based on the above hadith?

The hadith you mentioned is general (‘aam), and the Prophet (ﷺ) seeing Paradise is specific (khaas), so this is an example of specification of what is general (تخصيص العام).

Another way of looking at it is that the Prophet (ﷺ) did not see or hear Paradise, nor did it occur in his heart, before the event of Isra’ and Miʿraj; so the hadith does not include him, as it does not include Adam and Hawwa as well.

You could also refer the following link:

http://islamqa.info/en/140514

And Allah knows best.