Introduction to Linear Algebra, Gilbert Strang, 2016 (Wellesley-Cambridge Press) - A widely respected textbook providing a thorough treatment of linear algebra, including the definition and properties of matrix multiplication.
Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press) - This book's second chapter offers a clear explanation of linear algebra basics, specifically tailored for machine learning practitioners, including matrix operations and their role.
Linear Algebra (18.06SC), Gilbert Strang, 2011 (MIT OpenCourseWare) - An MIT OpenCourseWare resource offering video lectures and course materials on linear algebra, with a specific lecture dedicated to matrix multiplication.