sale_print_report/views/sale_voucher_print.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- <openerp>
    <data>
        <record id="views_sale_print" model="ir.ui.view">
            <field name="name">sale.order.print</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.invoice_form"/>
            <field name="arch" type="xml">
                <field name="number" position="before">
                    <div class="oe_right oe_button_box invoice_button_box" id="print_invoice"></div>
                </field>
            </field>
        </record>
	</data>
</openerp> -->