ITR-3 is the ITR Form to report business income. No documents are required to be attached while filing ITR-3 on the income tax website. Here is a list of required documents to prepare ITR-3.
PAN
Aadhar
Bank Statements of the financial year (1st April to 31st March)
Income related documents - Form 16 for Salary Income, Interest Statement, Rent Receipts, Capital Gains Statement, Trading Statement, etc
Form 26AS - You can download it from your account on the income tax website