Petetion Number partially printed on Visa Stamp

Hi,

Petetion Number has been partially printed on Visa Stamp, I do not have i-797 copy with me. Is there a way to get complete 13 digit number (EAC-97-237-xxxxx) ? My sponsor is requesting for me that I provide this complete number to him. How to get this last 5 digits number? Pls help.