When you receive the material

When you receive the material (PO)

Receving Valuation A/C Dr
                                                 AP Accrual A/C Cr

When you charge the resource to the WIP
WIP Resource A/C Dr
                                      Receving Valuation A/C Cr

For outside processing resources,
the default absorption account is the receiving valuation A/C (as defined in the receiving options.)
You should not change the default receiving valuation account.

from user guide
When you receive an outside processing purchase order, Oracle Purchasing credits the inventory AP accrual account, and debits the receiving valuation account.

Bills of Material then debits the work in process outside processing account and
credits the receiving valuation account. If you change the above default account,
your receiving valuation account will have an incorrect balance.