Is the questioner sinful for refusing to pay for the repair of a device after 3 years, even though the worker who installed the device verbally informed him of a 5-year warranty, and the written contract stipulates a comprehensive 5-year warranty, while the worker claims he made a mistake by not detailing it?

There are two types of warranties:

The first type: A warranty that is independent of the device's purchase and has a specified price. This is forbidden (haram (definition)) because it is based on gharar (definition) (excessive uncertainty) and gambling, as the Prophet (peace be upon him) forbade bay' al-gharar (sale involving excessive uncertainty). This type is considered a forbidden commercial insurance.

The second type: A warranty that is part of the device's purchase contract, whereby the manufacturer or seller undertakes to guarantee the device's soundness from manufacturing and technical defects and its fitness for operation for an agreed-upon period. This type of warranty is permissible (halal (definition)) according to Sharia (definition) and can be justified as: 1. A warranty for a defect that occurs to the buyer and is based on a cause existing prior to possession. 2. A warranty for a defect that cannot be known except through testing.

Based on this, if the device contract stipulates a five-year warranty, the seller or manufacturer has no right to demand payment for repairs during this period, in accordance with Allah's saying: "O you who have believed, fulfill [all] contracts," and the Prophet's (peace be upon him) saying: "Muslims are bound by their stipulations concerning what is permissible."