My wife wants to have sex with my friend, how do I approach this situation?

I have been with my wife for nearly a decade and she's the love of my life. She's an amazing woman, and I have no doubts at all about her. She's not cheating on me, this is just about exploring our sexuality. We have a very good friend, Tommy. Tommy is a very attractive guy and he and my wife have always been friendly and close. My wife, Sarah, has said that she would like to explore a sexual relationship with him. I trust them both, and I am open to this idea if it is something that he wants to do. How do I approach Tommy about this? It feels awkward.