When I refer to another post elsewhere, I quote the post and link to the original reference, like so:
Jack had an experience that might help you, which he posted in response to a similar question about widget X. Here's an excerpt:
When I was just a wee little lad, my Daddy brought to me a toy he made down at the lab; it filled me full of glee! A wonder to behold it was, with many buttons bright from the moment that I turned it on, it filled us all with fright!
It went ZAP! when it fired; it cursed when it missed and whirred as it took aim. It didn't know if we were friend or foe it attacked us just the same
It allows one to refer to the original answer, provides attribution, and helps people understand that this is not original material.
I suggest when this happens you edit the post if possible to comply with the above format. If you can't edit, or you choose not to, add a comment with a link to the original and flag it for moderator attention requesting that attribution be added to the post.