All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
From the perspective of Islamic Law, the buyer must take possession of the commodity in order to be allowed to sell it. This is clearly reflected in the Hadith where Prophet Mohammad(PBUH) said: "Whoever buys food let him not sell it until he takes possession of it. Ibn 'Abbas said: "I think the same applies to everything else as to food." {Narrated by Muslim}. From a juristic point of view, the buyer takes possession of the commodity by either actually taking it or by not being prevented from doing so at his convenience, and the latter is called "presumptive possession." In principle, custom determines how the buyer takes possession of the commodity, and this varies according to time and place. From the perspective of the Shaffii jurists, the possession of movables is achieved by the buyer`s actual reception of them; whereas, in immovables it is achieved through relinquishment. For further details, please refer to An-Nawawi`s book {Rawdat At-Talibeen/517}.
However, Hanfi and Hanbali jurists believe that possession of movables and immovables is achieved by relinquishment. In movables, it is achieved by the seller`s clear identification of the buyer`s commodity and his(seller) keeping it as a trust. For further details, please refer to Ibn Qhodama`s book {Al-Moghni. 4/85}.
Moreover, this view was adopted by the International Islamic Fiqh Academy, where it issued a resolution in this regard-during its sixth`s session-that read as follows: "Taking possession of different properties can be physical, such as taking them by hand, measuring, weighing(food), moving or transferring into the buyer`s possession. However, it can be presumptively achieved by relinquishment along with allowing the buyer to dispose of the commodity, even if he hadn`t actually received it. Moreover, possession of commodities varies according to their kind and the observed customs.
Moreover, among the contemporary forms of presumptive possession ratified by the Accounting and Auditing Organization for Islamic Financial Institutions{Standard No. 1/18}:
A-A bank record for the deposit of a certain amount into the client`s account in the following situations:
1- An amount is deposited in the client`s account directly or via a bank order.
2- The client concludes a matured exchange contract with the company in case of purchasing and selling exchanges.
3- The company deducts, by order of client, an amount from his account to add it to another account of a different currency in the company itself, or another, for the benefit of the client or another beneficiary. In addition, the company must observe the rules of exchange contract stipulated in Sharia.
B-Receiving the cheque which is covered by the currency indicated on it, and the amount was confined by the company.
C-The seller received the payment coupon endorsed by the credit card holder(buyer) in case the company issuing the card affords to pay that amount to the seller without any delay.
D-Receiving the documents ,such as the bill of lading, issued in the name of the recipient, which identify the commodities and the equipments in question, and authorizing him to dispose of them.
E-Categorizing commodities by one of the customary units of measurement, such as weighing and the like.
In conclusion, possession of a commodity is attained by the customer`s reception of it as well as by marking and keeping it as a trust with the seller. This is provided that it is actually identified in a certain spot of the seller`s store/shop, and that the latter can`t sell it or give it away. However, if these conditions aren`t met, then the buyer doesn`t possess the commodity that he had purchased, and so he isn`t permitted to sell it. And Allah knows best.