Join between Sales Order(SO) and Receivables(AR) in Oracle Fusion

SELECT *

  FROM ra_customer_trx_all rcta

      ,ra_customer_trx_lines_all ra

  ,doo_fulfill_lines_all l

 WHERE ra.interface_line_attribute5 = TO_CHAR(l.fulfill_line_id)

   AND rcta.customer_trx_id = ra.customer_trx_id

   AND rcta.trx_number = '123456789';

You can use INTERFACE_LINE_ATTRIBUTE5 column in RA_CUSTOMER_TRX_LINES_ALL which stores Fulfill Line ID of Sales Order.