Kulayb bin Shihaab Al-Kufi says that Abu Hurayrah Radiyallahu 'Anhu narrated to me the mubaarak saying of Rasulullah Sallallahu 'Alayhi Wasallam, that whomsoever sees me in a dream, has really seen me, because the shaytaan cannot impersonate me. Kulayb says, I mentioned this hadith to Ibn 'Abbaas Radiyallahu 'Anhu and also told him that I was blessed with the seeing of Rasulullah Sallallahu 'Alayhi Wasallam in my dream. At that moment I thought of Hasan bin 'Ali Radiyallahu 'Anhu. I said to Ibn 'Abbaas Radiyallahu 'Anhu that I found the image in my dream very similar to that of Hasan Radiyallahu 'Anhu. Ibn 'Abbaas Radiyallahu 'Anhu verified my statement, that truly Hasan Radiyallahu 'Anhu was very similar to Rasulullah Sallallahu 'Alayhi Wasallam in appearance.
App reference: Book 56, Hadith 4
English reference: Book 55, Hadith 392
Arabic reference: Book 56, Hadith 409