i believe it's only in some specific cases when both parties agreed to defer to religious laws.

could you please show me any law in israel, that gives blanket approval to civil courts to refer to holy texts if the law is not clear ?

Wow, that's wild! :-/

you know such a clause in a rental agreement would be legal in the US as well, right? Binding arbitration clauses are legal in rental agreements at least in many parts of the US and agreeing to a rabbinical court to be the arbitrator is legal as well.