Siman 497

(54.) It was very pleasing to him when someone merited to see him in a dream — even during his lifetime. And he said that there are people among his people who see him in a dream in the form of a great old man. And he said that if we were proper men as he desired, we could hear great and awesome things from him in dreams. And the main thing is to merit that what one sees and hears in a dream not be forgotten — for sometimes one sees and hears something and afterwards it is forgotten. (And this is because they take it away and snatch it from him upon return — as is cited in the holy Zohar, Bereishis...)