'Abdullah bin Mas'ud Radiyallahu 'Anhu reports that Rasulullah Sallallahu 'Alayhi Wasallam said:
"The one that has seen me in one's dream, has really seen me, as the shaytaan cannot impersonate me". (IT)
App reference (IT): Book 56, Hadith 1 (IT)
English reference (IT): Book 55, Hadith 389 (IT)
Arabic reference (IT): Book 56, Hadith 406 (IT)