This prohibition is supported by the Ayah:

﴿وَتَعَاوَنُوا۟ عَلَى ٱلۡبِرِّ وَٱلتَّقۡوَىٰۖ وَلَا تَعَاوَنُوا۟ عَلَى ٱلۡإِثۡمِ وَٱلۡعُدۡوَ ٰ⁠نِۚ﴾ "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." [Surah Al-Māʾidah: 2] ____ 3⃣. بيع المسلم على بيع أخيه Selling Over Another’s Sale An example of this is when someone says to a buyer who has purchased an item for a set price, “I will sell you the same item for a lower price,” or “I will sell you a better-quality item for the same price.” This practice is prohibited based on the hadith narrated by Ibn Umar (may Allah be pleased with them both): The Messenger of Allah (peace and blessings be upon him) said, ((ولا يبع بعضكم على يبع بعض)) “Do not sell over another’s sale.” [Narrated by Bukhari & Muslim] ____ 4⃣. الشراء على الشراء Buying Over Another’s Purchase An example of this is when someone says to a seller who has agreed on a price with a buyer, “Cancel the sale, and I will purchase it from you at a higher price.” This practice falls under the prohibition mentioned in the previous hadith. ____ 5⃣. بيع العِينة - (The ’Ēnah Sale) This type of transaction is prohibited due to its underlying resemblance to riba. The process involves a person selling an item to another for a deferred price, and then repurchasing it from the buyer for an immediate, lower cash price. Consequently, the buyer ends up with cash and owes the seller the higher deferred price. For example, a person sells a piece of land for £50,000 to be paid after a year, then repurchases the same land from the buyer for £40,000 in cash. At the end of the year, the buyer remains liable for the original £50,000. The term "’Ēnah" derives from the fact that the buyer effectively receives cash in place of the commodity. This practice is prohibited because it is a deceptive means to engage in usury. Ibn ’Umar (may Allāh be pleased with him) narrated that the Messenger of Allah ﷺ said: (إِذَا تَبَايَعْتُمْ بِالْعِينَةِ، وَأَخَذْتُمْ أَذْنَابَ الْبَقَرِ، وَرَضِيتُمْ بِالزَّرْعِ، وَتَرَكْتُمْ الْجِهَادَ، سَلَّطَ اللهُ عَلَيْكُمْ ذُلًّا لَا يَنْزِعُهُ حَتَّى تَرْجِعُوا إِلَى دِينِكُمْ)) “When you engage in ’Ēnah transactions, cling to the tails of cattle, and abandon jihad, Allah will strike humiliation upon you that will not be lifted until you return to your religion.” [Narrated by Ahmad, 28/2, Abu Dawood (3462); authenticated by Sheikh Albani in Silsilat As-Saheehah, No. 11] NOTE: Sheikh Ibn ’Uthaymīn (may Allāh have mercy on him) said: «إذا حضر بائع السيارة إلى مكان بيعها واشتراها بأكثر من الثمن الذي باعها به جاز له ذلك، أما إذا اشتراها البائع الأول بنفس الثمن، جاز له ذلك. أما إذا اشتراها بأقل من الثمن الذي باعها به فهذا لا يجوز؛ لأنَّها تكون هذه هي العينة» "If the seller of a car comes to the place where it is being sold and buys it for a HIGHER price than what he sold it for, this is permissible. Similarly, if he purchases it for the SAME price at which he sold it, this is also permissible. However, if he buys it for a LOWER price than what he originally sold it for, this is not permissible, as this would constitute an ’Ēnah transaction." BENEFIT: Selling the item for cash at a lower price is permissible if one sells it to other than the original seller. This is known as التورق! ____ 6⃣. بيع المبيع قبل قبضه Selling Goods Before Taking Possession It is prohibited to sell a purchased item before taking full possession of it. For example, if a person buys an item but resells it to another party before physically receiving or taking control of it, the transaction is invalid. Abu Hurairah (may Allāh be pleased with him) narrated that the Messenger of Allāh ﷺ said: ((من ابتاع طعامًا فلا يبعه حتى يقبضه)) “Whoever buys food should not sell it until he has taken possession of it.” [Agreed upon: Bukhari (2136) Muslim (1525)]