To prove ownership of a property in India, several legal documents are essential, and as a lawyer, I emphasize the importance of having clear and valid documentation to establish and defend property rights.

1. Sale Deed / Conveyance Deed:
   This is the most critical document that legally transfers ownership of the property from the seller to the buyer. It must be executed on a stamp paper of prescribed value, signed by both parties, and registered under the Registration Act, 1908. The registered sale deed serves as conclusive proof of ownership.
2. Title Deeds:
   Title deeds include any documents that establish the ownership chain of the property, such as earlier sale deeds, gift deeds, partition deeds, or wills through which the current owner derived the title.
3. Property Tax Receipts / Municipal Records:
   These receipts show payment of property tax to local municipal authorities and indirectly support ownership claims, demonstrating possession and control over the property.
4. Encumbrance Certificate (EC):
   This certificate, issued by the sub-registrar’s office, confirms that the property is free from any legal or monetary liabilities like loans or mortgages. It traces the history of ownership transactions.
5. Possession Documents:
   These include possession letters, allotment letters, or rent receipts in case of leasehold properties. They show actual physical possession and occupation.
6. Mutation Records:
   Though mutation entry in revenue or municipal records does not confer ownership, it shows that the government records have been updated to reflect the current owner’s name.
7. Khata Certificate / Extract:
   Particularly in urban areas like Bengaluru and some other cities, the khata certificate is an important document for property tax and municipal purposes. It shows the property is recorded in the name of the owner in municipal records.
8. Patta / RTC (Record of Rights, Tenancy, and Crops):
   For agricultural land, the Patta or RTC issued by the revenue department is a crucial document evidencing ownership and rights over the land.
9. Will or Gift Deed:
   If the property is acquired through inheritance or gift, the registered Will or Gift Deed proves ownership transfer from the previous owner.
10. No Objection Certificates (NOCs):
    In certain cases, like cooperative societies or housing societies, NOCs from the society or local authorities might be required to validate ownership rights.

Possession of these documents, especially the registered sale deed, is legally necessary to prove ownership and defend against any disputes or claims related to the property.