Sleeping like one, do you go by the book? (3)
I believe the answer is:
log
'the book?' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for log that I've seen before include "A ship's journal" , "Written account of a voyage" , "Bulky piece of wood" , "Piece of cut wood" , "Ship's record" .)