Is the pledging (Rahn) of an unknown item valid?
General Chapter
Al-Mughni
Book of Pledges (Collateral)
Primary text
The pledging of an unknown item is invalid because its sale is invalid. For example, pledging an item stating, "I have pledged this sack, or house, or map along with what is inside it," is invalid due to the ambiguity (Jahalah). The validity in pledging requires the same conditions necessary for a valid sale, including the ability to take possession (Taslim). Therefore, pledging a runaway slave (Aabiq) or an escaped camel (Jamal Sharid), or that which is not owned, is invalid.
Supporting text
If one pledges a container, such as a sack, without stipulating 'along with what is inside it,' the pledge is valid due to the known nature of the container itself, unless the contents are negligible in value, such as an old, worn-out sack.