You generally don’t need permission from the website owner to link to the home page of their website, but it is a good idea to ask.
You need permission from the website owner to link to a page within their website (for example, to an article that is published on the site).
Have a look at this example of an email or letter asking permission to use a work (.doc 26 kB) that appears on a website:
This is an example of an email or letter asking permission to link to a work (.doc 26 kB) that appears on a website: