Shama-il Tirmidhi Chapter 055, Hadith Number 006 (394).

Abu Qataadah Radiyallahu 'Anhu reports that Rasulullah Sallallahu 'Alayhi Wasallam said: "Whomsoever sees me, that is, in a dream, has seen that which is a fact".

Commentary
Meaning one has really seen me. It cannot be so that the shaytaan shows something else and says that it is Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam. Some of the 'ulama have written that it means, it is a true dream and not a collection of thoughts.