Is selling something for a deferred payment with a discount for cash payment considered "two sales in one sale"?

The Messenger of Allah, peace and blessings be upon him, prohibited two sales in one sale. Al-Khattabi explained this in two ways: one is that the seller says: "I sell you this garment for ten [dirhams] in cash, or for fifteen [dirhams] on credit." This is impermissible due to the ambiguity of the price. Simak explained it by the seller saying: "It is for such and such a price on credit, and for such and such a price in cash."

Similarly, Al-Shafi'i explained it by saying: "I sell it to you for a thousand in cash or for two thousand payable in one year, so take whichever you and I wish."

If an agreement is reached between the seller and the buyer before concluding the contract that if the payment is expedited, the price will be such and such, this falls under "two sales in one sale." However, if the agreement is reached after concluding the contract, this does not fall under the prohibition, but it falls under the issue of "forgo [part of the debt] and expedite [payment]," which is not permissible according to the four Imams and others, due to the presence of usury therein.