Find a commit on GitHub given the commit hash

View single commit:
https://github.com/<user>/<project>/commit/<hash>

View log:
https://github.com/<user>/<project>/commits/<hash>

View full repo:
https://github.com/<user>/<project>/tree/<hash>

<hash> can be any length as long as it is unique.

A URL of the form https://github.com/<owner>/<project>/commit/<hash> will show you the changes introduced in that commit. For example here's a recent bugfix I made to one of my projects on GitHub:

https://github.com/jerith666/git-graph/commit/35e32b6a00dec02ae7d7c45c6b7106779a124685

You can also shorten the hash to any unique prefix, like so:

https://github.com/jerith666/git-graph/commit/35e32b

---

I know you just asked about GitHub, but for completeness: If you have the repository checked out, from the command line, you can achieve basically the same thing with either of these commands (unique prefixes work here too):

git show 35e32b6a00dec02ae7d7c45c6b7106779a124685
git log -p -1 35e32b6a00dec02ae7d7c45c6b7106779a124685

Note: If you shorten the commit hash too far, the command line gives you a helpful disambiguation message, but GitHub will just return a 404.