How do you use the `@include` to use a Font awesome icon in you sass file.

E.g - If I wanted to use this icon:
<http://fortawesome.github.io/Font-Awesome/icon/pencil/>

I understand that you can use it in your HTML like this:

```
<i class="fa fa-pencil"></i>

```

However I want to be able to do the following or something similar:

```
.class-name {
    @include: fa-icon(fa-pencil);
}

```

What is the default/proper way to do this?