I would make him realize that pages  are very important because t is made by cutting a tree . Save tree ,save life"
if he will countiniously tear the pages then think he is not only wasting the paper but a TREE which is very essential in our life. so it is very bad habit and also deforestation . so do not tear the pages. hope u understood.. :))
You should first enquire him for what he is doing so.if the reason behind is unnecessary then you should advise him in the proper should try to make him realise that it is not a good thing to do so and that, useful things are never to be wasted