Is it permissible to set two prices for a commodity: one if paid in cash, and another if paid in installments?

If the seller says: "This car is for fifty thousand in cash, and sixty thousand in installments," then the sale has two scenarios:

1. Permissible: If the seller and buyer agree on a specific price and payment method before they part ways.

2. Forbidden and invalid: If they part ways without agreeing on the price, which is known as "two sales in one sale," and was forbidden by the Prophet (peace be upon him), due to the instability of the price and the consequent ambiguity and dispute.