Declaration

I need to write a declaration stating that someone has been working for me. I know the person I'm sending a letter to.
Can I use this form?

Dear Mr (name),

I hereby declare that..

Your sincerely,
...

Thanks in advance!

[Anglika]

As you give it, that's a bit uninformative. Even if he knows you, the recipient will need to know when this person worked for you, how long, and possibly also the kind of work that they carried out for you.