User Exit/ BADI during creation of vendor master

Dear Friends,

During creation of vendormaster if the with holding tax is maintained then PAN no. field should be made mandatory.

So far I know this can't done through standard field selection of vendor master. So this is to be done through BADI/User exit. Please provide me the same where in run time I can get PAN no field. It comes from the excise table.

Regards