How do i turn of preview message on whatsapp and bbm?

I have a samsung galaxy s5 ive recently had an update to the new lollipop but i have whatsapp and bbm and everytime i have a message off bbm or whatsapp it shows a preview of it on my screen and i hate that especially when someone is using my phone there able to see part of the message i want the notifaction bit but dont want it to show part of the message on my screen please how do i turn it off?? Ive tried to find a way but cant its annoying me i can do it on messages but not on bbm or...

How do i turn of preview message on whatsapp and bbm?

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