<strong>bootstrap</strong>/templates/post.tmpl#L44 is where @ralsina copied that from.  That thing is bootstrap-specific.

The line you wanted to use is:

```html
<p class="sourceline"><a href="${post.source_link()}" id="sourcelink">${messages("Source")}</a></p>
```

There is a source<strong>line</strong> class and a source<strong>link</strong> id.  The former is not reproduced because we’re not in base and it’s for the `p` (bootstrap uses an ordinary right-side-menu item); the latter is nicely available in both.