The reign of Caliph Uthman b. Affan is known for

Caliph Uthman b. Affan's reign is primarily known for the standardization of the Qur'an. During his reign, he ordered the compilation of a standardized version of the Qur'an, which was based on the original manuscript compiled during the time of Prophet Muhammad (PBUH). This standardized version was then distributed throughout the Islamic empire, ensuring that all Muslims read the same version of the holy book. While Uthman did focus on tax collection and administrative fairness, these actions were not as significant as the standardization of the Qur'an. Uthman also played a role in the collection and preservation of Hadith, but this was not the primary focus of his reign. Overall, Uthman b. Affan's reign is primarily remembered for his efforts in standardizing the Qur'an, which has had a profound impact on the Islamic world to this day.