BuddyPress.org

<div class="item-avatar">

<a href="<?php echo bp_core_get_userlink( $user->user_id, false, true ) ?>">

<?php echo bp_core_get_avatar( $user->user_id, 1 ) ?></a>

</div>

The above is from bp-core-directory-members.php. You’ll have to put `$post->post_author in there.