What is the legitimate Islamic view and the evidence regarding the permissibility of increasing the price in an installment sale over the price of a spot sale, taking into account the Prophet's saying, peace be upon him, "Whoever makes two sales in one sale" and the story of Barirah?

The correct view is that it is permissible to sell by installments at a price higher than the spot price, and scholars have adduced the following as evidence:

The generality of Allah's Almighty saying: {O you who have believed, when you contract a debt for a specified term, write it down.} The Prophet's, peace and blessings be upon him, command to Abdullah ibn Amr ibn al-As to equip an army, whereupon he would buy a camel for two camels (paid) at a later date. The Prophet's, peace and blessings be upon him, approval of the sale of Barirah by installments over nine years. Installment sale is similar in meaning to salam sale (advance payment for future delivery), which is permissible by scholarly consensus.

However, installment sales must adhere to the following Shariah controls:

Both parties must definitively agree on an installment sale rather than a spot sale. The terms, price, and installments must be known. No interest or penalty should be charged for delayed payment. The commodity must be in the seller's possession before the contract.