If one of your friends sends you a Facebook request asking you to connect on Facebook don’t open it. It’s spam of the very worst kind.
The request seems fairly legitimate in its design, but if you actually take a look at the URL it leads you to, there’s absolutely no evidence that the product has any ties to the mobile messaging service.
According to The Next Web, the goal of the scam is to get hold of your Facebook information. From there it will spread to all your friends.
And just to make doubly sure you don’t click on anything purporting to be from Whatsapp, you should be aware that the company doesn’t actually have a Facebook app. Not that there aren’t a slew of pretenders out there: