Shaykh Al-Islam Ibn Taymiyah and others said that it is possible for a person to see Allah in a dream. A person may see in his dream that Allah is speaking to him, but whatever images he sees is not Allah because there is nothing like unto Allah, so there is nothing that resembles Him.

It is possible for a person to see the Prophet (peace and blessings of Allah be upon him) in a dream, and the Shaitan cannot appear in the image of the Prophet (peace and blessings of Allah be upon him), but he could appear in another form and claim that he is the Prophet (peace and blessings of Allah be upon him).

Interpretation of dreams in Islam falls into various categories: 1- Dreams may be interpreted in light of the Quran, 2- or in light of the Sunnah, 3- or by means of the proverbs, 4- or by names and metaphors, 5- or in terms of opposites. For more, please see the detailed answer.