Hisnul Muslim is a well-known book of supplications (duas) and remembrances (azkaar). It contains a comprehensive collection of authentic prayers and invocations from the Quran and the Sunnah (traditions of the Prophet Muhammad, peace be upon him). It is also referred to as the "Fortress of the Muslims."
(Authored by Arab scholar, Sa'id bin Ali bin Wahf Al-Qahtani, originally published in 1989)