Primisory note

I gave 2.55 lacs to My uncle for his Daughter's marriage. I asked him to return it in next 5 years. The amount is paid by cheques. I want to make some legal document so that my Uncle and his son will not change their promise to return the amount. He shaould not dely beyond 5 years. wha t will be the best document to creat so that I can get mey anout back? Thanks.