His refer to the book was helpful.

A mention or reference to something.
Her refer to the meeting was important.
I appreciate your refer to my work.
Please make a refer to the guidelines.
direct refer
frequent refer
quick refer
reference
citation
mention
Please refer to the manual for instructions.

To mention or direct someone to a source of information.
You should refer to the website for more details.
Please refer your questions to the teacher.
I will refer you to a specialist for further help.
refer to a source
refer to a document
refer to a study
direct
point
guide