Family and marriage. For example, when getting married, any promise made by both men and women must be fulfilled. Mu Sheng (peace be upon him) said: The promise in the engagement is very important and must be fulfilled. Mu Sheng (peace be upon him) is also opposed to revealing the ambiguous relationship between husband and wife to outsiders.
2) friends. If someone sends a message to a Muslim asking for confidentiality (confidentiality is a prerequisite), then the Muslim shall not breach the contract except in special circumstances (discussed below).
3) debt. Paying off debts is also a form of keeping promises. In addition to force majeure such as natural and man-made disasters, Muslims must pay their debts as promised. Mu Sheng (peace be upon him) said that even the sins of martyrs can be forgiven, except for his outstanding debts. Because paying off debts is a sign of keeping promises. In addition, Muslims must return the stored goods and property to their original owners.
Reference: Koran 4: 58