Whosoever saw the Messenger of Allah (Allah bless him & give peace) in a dream, the dream is true and genuine. It is not merely an imagination. The Shaytan cannot come in ones dream and portray to be the Prophet Sallallahu Alayhi Wasallam. (All three interpretations related by Mulla Ali al-Qari in his al-Mirqat, 9/24).
The scholars have differed as to whether the dream is true in the case where one does not see the Messenger of Allah (Allah bless him & give him peace) in his recognized features and qualities, that have been transmitted in the traditions.
Some scholars are of the view that the dream will only be true and genuine if the person sees the Prophet of Allah (Allah bless him & give him peace) in his recognised features. This opinion has been attributed to Qadi Iyad.
The majority of the scholars, however, including Imam Nawawi, are of the view that if a person dreams the Messenger of Allah (Allah bless him & give him peace) then his dream is true, regardless of whether he sees him on his recognized features or otherwise.
If a person was to see the blessed Messenger of Allah (Allah bless him & give him peace) in his unrecognized features, for example, he saw him without a beard, or with full grey hair, etc? then this dream will need to interpreted.
The differences in appearance may be due to the good or bad habits of the dreamer. According to the variation of people?s personalities, their dreams differ. Some dream him old, whilst others dream him young. Some see him pleased, whilst others see him disturbed. Therefore, the dream will need to be interpreted by a person who is qualified in this field, and who has taqwa and piety
(Mulla Ali al-Qari, Mirqat al-Masabih, 9/25).