Rabbits in house

We just moved into the Netherlands when your apartment and in the contract it’s mentioned that we cannot have pets. We have two Dutch Rabbits and a lot of friends told us that it’s OK with they don’t need to mention it to the landlord after a few months we will gain trust that we pay on time and so on that we can ask to bring a rabbit. Do you think it’s illegal for the ( Landlord ) to say we cannot have Rabbits?
What should we do?