Dear Mohammed,
we can call your requirement as IPO process. In IPO process we procure finished goods from the vendor and we deliver to customer.
Configuration is like this,
1.Create material like third party material only(select purchasing view and mention purchasing or and group) in sales org 2 view mention item category group as BANC to determine item category TAB.
1.In TAB item category mention special stock indicator as 'E'.
2.In CB schedule line category maintain controls like this.
order type : NB
Movement Type: 601
Item category: 0
Account assignment category: E
3. Requirement class for IPO process is KEB.
In KEB requirement class maintain controls like this
Special stock indicator: E
Account assignment category: E
while creating sales order check whether requirement type KEB is determining or not (in procurement tab)
Do this configuration as it is you can get expected result