Is one legally obliged to sell a car with a purchase contract?

Hello together, quick question: If you sell an old car for 200 or 300 euros to an export buyer, you are legally obliged to create a purchase contract, or can you simply exchange money for car + papers and is good? Please only secure information. If you have assumptions, you can write this, but not sell as a fact, but point out that it is only your own opinion / guess.