Siman 171

(5.) There was yet another book of his — even higher and higher than the burned book — and that is the Hidden Book. And he said that even his own body withdrew when he wrote it, and that book has never been seen by any eye. And he said it is of the aspect of razin d'razin [secrets of secrets] — meaning, as it appears to him, compared to the other matters he reveals. And he said that Messiah will explain it. And this Hidden Book was already completed by him at the beginning of the year 5566 (5567) — five years before his passing. And now stand and contemplate — to what level he reached afterwards. For he never stood on one level his entire life — and literally at every hour and hour he attained new things according to his awesome level. And understand this very, very well — for the level of the greatness of the Hidden Book is beyond any thought whatsoever — and Messiah will explain it. And from now contemplate and estimate in your mind his greatness, for he lived afterwards five full years — with difficult and severe sufferings — and was in all the towns and the displacements of the journeys to Navoritch and afterwards was also in Brod and Lemberg — through all of which he acted and accomplished very much. And now stand and contemplate — to what level he attained afterwards! For he never stood still at one level until the day he passed on — and literally every single hour he attained new things according to his very awesome level. And understand very very well — for the greatness of the Hidden Book cannot be grasped by any thought whatsoever, and Mashiach will tell its interpretation. And from now you shall contemplate and estimate in your mind its greatness etc.