git-commit(1) Manual Page, The Git Community, 2023 - This is the official and most authoritative source for the git commit command, detailing all its options and behavior.
Pro Git (Chapter 10: Git Internals - Git Objects), Scott Chacon, Ben Straub, 2014 (Apress) - This section explains the low-level mechanics of Git commits, detailing how commit objects, trees, and blobs are created and linked to form the project history.