The Kitāb al-Istiqamah by Abu Sa'id Muhammad b. Sa'id Al- Nā'bt Al-Kudami is one of the richest books in Ibadhi thought dealing with the science of al-Walāyah wa-l-Bara'ah (Loyalty and Disavowa!) The book was written as an answer to those who rejected the truth about the unrest occurring after the resignation of Imam al-Salt b. Mālik from the Imamate, when both Masa b. Mūsā and Rashid b. al-Nadir dissented from him. The author defended the requirements and conditions of the requirements of al-Walāyah wa-t-Barā'ah and explained and analysed their provisions in detail. The research aims to identify the scientific contribution of Abu Saeed Al-Kadmi through the Book of The Kitāb al-Istiqamah to bring it out as the author wanted it and with the scientific addition that he added, and the relation of what he has addressed regarding the provisions of what some of our contemporary time scholars consider of others as being unbelievers. The thesis includes the study of the book and the methodology followed by the author in addition to the investigation from the beginning of the third part of the manuscript. In this study I followed the scientific method in manuscript editing in terms of comparing the different manuscripts, inserting footnotes, takhrij, identifying names, and others. I divided the study into two sections, Section one is about the author and the Kitāb al-Istiqamah. It contains three parts; the life of the author, the study of the book, the method of investigation. The second section is an investigation from the beginning of the third part of pages B7 to 405 of the manuscript 'making three-quarters of the book in thirty-nine chapters. At the end of the study, the conclusion stated the most important results and recommendations that shows Al-Kadmi was a well versed scholar in issues of al-Walāyah wa-l-Barā'ah (Loyalty and Disavowal, in which he dealt with details of its various provisions and ramifications, and established a thorough synthesis through the legitimate (Sharia) evidence and the development of the various provisions associated with it. The fundamentalist and jurisprudential (Figh) rules were clear in his approach to this book, as well as his openness to the statements of other doctrines (Mathahib) of thought which he mentions without attribution to their owners and discusses them and follows the evidence of nonfanaticism of a certain doctrine (Mathhab). He disagreed his contemporaries on various issues in his book of Kitāb Istiqamah as well as with scholars of his own doctrine (Mathhab).