Dear Sir or Madam,
I appreciate for your proposal, but I cannot accept your offer.
I think that position is not interest for me, because I have more fascinate and responsible job right now.
I also fully satisfy with my job, so do not interest in changing it.
I have an agreement with my employer that means I cannot leave my job for three years.
Nevertheless, it is a good offer, so I would like to give to you my reference for a few people whom I been dealing with.
The first person is Dmitry.
He has five years of experience in your field.
He is a reliable and a hard-work employee.
As far as I know, he is stack for 3 years in the current position and he think about changing a company.
Jon is my second reference.
He has 5 years of working experience and degree in science.
If you are interested, I give you their contacts data.
Yours faithfully, Eugene.