— the sale of a fetus still in the womb;
— the sale of a runaway slave or stray animal;
— anything that has not been seen and has not been properly described;
— the sales known as mulāmasa (concluded merely by touching the goods) and munābaza (concluded by one party casting an item to the other);
— and, in general, every contract marred by obvious uncertainty. In such cases one of the two parties will inevitably come out either a winner or a loser, and this conflicts with the very purpose of exchange, which is that the consideration should match the item exchanged on terms equally understood by both sides. Whenever the price or the object of sale is unknown, or the term of a debt is left undefined and indeterminate, the deal enters the realm of gharar and maysir that Allah has prohibited.

Among the other forbidden pitfalls in transactions are:
— injustice;
— cheating;
— deceptive practices and the concealment of defects; and
— diminishing measures and weights, or otherwise curtailing people’s rights in taking or giving—by seizing more than one is due or paying less than one owes. This is among the gravest of prohibitions, and Allah has threatened the perpetrators with punishment in this world and the next, having destroyed an entire nation because of this vile practice.

All of these unlawful dealings fall under His words: “Do not consume one another’s wealth unjustly” (Qur’an 4:29), a ruling that also encompasses usurpation, theft, and the like.