How can I reference a commit in an issue comment on GitHub?

Answer above is missing an example which might not be obvious (it wasn't to me).

Url could be broken down into parts

https://github.com/liufa/Tuplinator/commit/f36e3c5b3aba23a6c9cf7c01e7485028a23c3811
                  \_____/\________/       \_______________________________________/
                   |        |                              |
            Account name    |                      Hash of revision
                        Project name              

Hash can be found here (you can click it and will get the url from browser).

Hope this saves you some time.

To reference a commit, simply write its SHA-hash, and it'll automatically get turned into a link.

See also:

• The Autolinked references and URLs / Commit SHAs section of Writing on GitHub.

Just paste the commit referencing link in the comment github automatically mentions the commit on the comment.