Charles Ellicott Commentary Deuteronomy 9:9

"When I was gone up into the mount to receive the tables of stone, even the tables of the covenant which Jehovah made with you, then I abode in the mount forty days and forty nights; I did neither eat bread nor drink water." — Deuteronomy 9:9 (ASV)

I neither did eat bread nor drink water. —This fact is not related in Exodus concerning the first forty days which Moses spent in Mount Sinai “with his minister Joshua.” It might be supposed or implied, but it is not recorded.