As you may know, there are ads on Facebook. Quite a lot actually. So with that in mind, the following really shouldn't be all that surprising. The social network is working on bringing ads into its own-brand chat app, Facebook Messenger. These will show up inside the home screen of Messenger, where you currently see your most recent chats. The look of the ads will be tightly integrated into the design of the app so that they don't stand out too much, but the amount of vertical space they take up (which is roughly equivalent to three chats) will definitely not go unnoticed, as you can see...
Source: http://www.gsmarena.com/ads_are_coming_to_facebook_messenger_brace_yourselves-news-26135.php