As for the sale of blood and purchase of blood in our times...

As for the sale of blood and purchase of blood in our times, which is used to save the injured and sick, then, it is permissible. Likewise is the sale of guard dogs and hunting dogs. The sale and purchase of usurped things except when its owner has endorsed the transaction. The sale and purchase of things that have unlawful advantage like the instruments of gambling and similar examples.

The sale and purchase of something that has no value in the common perception although it may possess a value with specific individuals, like many insects. Transactions in which there is interest (Ribaa). The sale and purchase of counterfeited and adulterated commodities when the purchaser is unaware of its state, like selling milk mixed with water or oil mixed with fat or something else. This action is called cheating (Ghashsh) and it is a major sin.

It has been reported that the Messenger of Allah, Blessings be upon him and his family said: “He who cheats a Muslim or harms him or deceives him is not from us.” Issue 727: There is no objection in selling the Mutanajjis (commodity). The Mutanajjis commodity is that which has contacted Najaasah (impurity) and it is possible to purify it or use it, like fruits, fabric and carpets.

However, when the purchaser intends to use it for eating, or acts that have purity (Tahaarah) conditional for them, it is obligatory to inform (the purchaser) to avoid it. Issue 728: When something pure becomes impure with that which it is not possible to purify, like oil, if it is used only for eating, then, its sale is invalid and unlawful. As for when it has other uses not having purity condition in them, then, its sale is proper (like impure petroleum).

Issue 729: Edible commodities and its likeness imported from non-Islamic countries, when their impurity is not certain and incontestable, there is not objection in their sale and purchase. Like when it is likely that milk and cheese and oil is prepared and produced by means of an automated process without hands being entered into it. Issue 730: The sale and purchase of meats and fats supplied from non-Islamic lands or taken from the hand of a non-Muslim is invalid.

Likewise are hides (leathers) according to precaution. However, there is no objection when it is known that it is from animals slaughtered in a legal manner or under the supervision of Muslims. Issue 731: There is no objection in selling and purchasing meats and fats taken from the hand of Muslims.