gistfile1.rb

# routes.rb
resources :clients do
  resources :payments
end

# views/clients/index.html.haml
= link_to 'New Payment', new_client_payment_path(client)

# controllers/payments_controller.rb
  def new
    @payment = Payment.new
    respond_to do |format|
      format.html # new.html.erb
    end
  end

  def create
    @payment = Payment.new(params[:payment])

    respond_to do |format|
      if @payment.save
        format.html { redirect_to(root_path, :notice => 'Payment was successfully created.') }
      else
        format.html { render :action => "new" }
      end
    end
  end