This treatise by Imam Ahmad ibn Hanbal, the deeply knowledgeable Imam of the Hanbali school of juristic reasoning, was written several hundred years ago for the benefit of the inhabitants of a town where the Imam stayed for a period of time. It takes the form of a letter or a speech addressing the townsfolk, and contains a complete, clear description of the prayer. It includes detailed observations of the mistakes which Imam Ahmad observed during his time in that town. It was and remains an invaluable work for all Muslims, detailing many common errors made during prayers, some of which are serious enough to invalidate the act of worship. The book includes explanatory notes by the translator, Sameh Strauch.