Ibn Majah

Benefits and Issues:

➊
All forms of deception in sales are included in this, in which the quantity of the item being bought or sold cannot be estimated. For example:
The sale of fish in a river, or the buying and selling of the unborn offspring in the womb of a female animal.

➋
If, along with a permissible item, something whose reality is unknown is also being sold incidentally, then it is permissible. For example, if a pregnant animal is sold, then its unborn offspring in the womb is also sold along with it, even though selling it separately is not permissible, but its sale with the mother is valid.
Similarly, when selling a house, its foundations are also sold along with it, even though it is difficult to ascertain how deep or thick they are.

➌
The sale by pebbles refers to those forms of lottery that were prevalent in that era. For example:
A shopkeeper tells a customer to throw a pebble, and whichever item the pebble lands on, I will sell you that item for one hundred rupees, even though those items differ in quantity, quality, and value.
In today's era, many forms of lottery are prevalent, such as some companies launching prize schemes to increase the sale of their products.
All of these fall under the ruling of "sale by pebbles."

➍
One form of sale by pebbles in the Age of Ignorance was also this: you throw a pebble, and wherever the pebble lands, I will sell you that much land for such-and-such price.
This is also prohibited.