I saw a question about how the piece of Voldemort's soul would be affected if Harry broke the Unbreakable Vow but it doesn't say what the Unbreakable Vow in question was.
I can't remember or find anything about Harry making one, so did he?
I have seen some speculation on having to make them for the Triwizard Tournament but as far as I am aware, this is untrue. However, I could be wrong.
There's only one instance in the Harry Potter books (and films) where an unbreakable vow is made, that between Narcissa Malfoy and Severus Snape in Harry Potter and the Half Blood Prince.
Harry doesn't ever make the vow, although he and Ron do discuss it.
Ron Weasley: "An Unbreakable Vow? Nah, he can't have...Are you sure?"
Harry Potter: "Yes, I'm sure. What happens if you break it?"
Ron Weasley: "You die."
The question you've referenced is more of a "what if" style of question, speculating about the likely effects if Harry (a sorta horcrux) had broken an unbreakable vow, rather than an actual instance from the films or books.
