'Mask a part of Field number using logstash and copy Original Field

I was looking for information about masking fields in logstash and I got the following solution:

 filter
  {
   mutate {
    gsub => [
     "message","[0-9]{16}","################"   
   ]
   }
 }

however I didn't want to lose the original content field, how do I copy the old content?

logstash elastic-stack

Sources

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