Q. I found a really useful source and I have problems in referencing it because it is a sample chapter. Furthermore, no date is stated.

The source you are referencing would fall under the category 'Using electronic resources' subheading 'Publications available from websites' from our guide to Harvard referencing guide: 

At the bottom of the guide there is a section about how to deal with 'References with missing details' which will give you advice on what to do when the date is missing.

For more information, please use the Anglia Ruskin Harvard Guide