Restrict purchase request (source = external) in case of internal availability of the item

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Hello all, please, i would like to check if you are aware of any way for achiving that behavior : 

Users have access to create requisition for both sources : external (suppliers) and internal (inventory). 

The goal is to , in case an item 'A' is available internally, do not allow the user to request it from external source. 

Is there any way to achieve that dynamism ?

 

KindRgds