voucher_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
<data>

        <!-- Supplier Payment -->
        <record model="ir.ui.view" id="view_vendor_payment_form">
            <field name="name">account.voucher.payment.form</field>
            <field name="model">account.voucher</field>
            <field name="inherit_id" ref="account_voucher.view_vendor_payment_form"></field>
            <field name="arch" type="xml">
                <xpath expr="/form/sheet/notebook/page/field[@name='line_dr_ids']/tree/field[@name='move_line_id']" position="after">
                    <field name="supplier_invoice_number" />
                </xpath>
                <xpath expr="/form/sheet/notebook/page/field[@name='line_cr_ids']/tree/field[@name='move_line_id']" position="after">
                    <field name="supplier_invoice_number" />
                </xpath>
            </field>
        </record>
    </data>
</openerp>