Are you in the UK? Only it's just a legal requirement for all horses, ponies and donkeys to have one before they are 6 months old and you are only meant to buy a horse who has one. This is also to prevent stolen animals being sold. You can also get a hefty fine for having a horse/transporting one without a passport. There are a number of agencies who provide passports. I would google it and select one ASAP. Good luck!