Pattern Recognition and Machine Learning, Christopher M. Bishop, 2006 (Springer)DOI: 10.1007/978-0-387-45528-0 - This classic textbook covers the fundamental principles of machine learning, including model evaluation, generalization, and the use of validation sets for model selection and hyperparameter tuning.
Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press)DOI: 10.7551/mitpress/9780262035613.001.0001 - Chapter 5 ("Machine Learning Basics") offers an authoritative explanation of generalization, overfitting, underfitting, and the role of training, validation, and test sets in deep learning contexts, applicable to general machine learning.
CS229 Lecture Notes: Supervised Learning (part 2), Andrew Ng, 2019Stanford University CS229 - These widely used lecture notes from a foundational machine learning course explain data splitting for model evaluation and selection in an accessible manner.
Hands-On Machine Learning with Scikit-Learn, Keras, and TensorFlow, Aurélien Géron, 2022 (O'Reilly Media) - This practical guide explains the importance of train/validation/test sets for building and evaluating machine learning models, with clear examples of how to implement the split. (3rd edition)