Крепость мусульманина is an Islamic reference app developed by IslamBooks. The app is available on Android and is free to download. The app's name is derived from the words of remembrance of Allah mentioned in the Quran and Sunnah. The app is an excellent reference source for hadiths, and it provides the sources of the hadiths as well as their numbering. The app also includes information on the weakness of some hadiths. The app developer, Abu 'Ubaidullah, has done an excellent job of providing an easy-to-use interface for users to access this important information.

The app is a must-have for those who want to learn more about Islam and its teachings. It is a valuable resource for scholars, students, and anyone interested in the religion. The app is regularly updated, ensuring that users have access to the latest information. Overall, Крепость мусульманина is an excellent app that provides accurate and reliable information on Islam and its teachings.