git rebase -p

Sorry, this isn't the same as git [checkout|stash|reset|add] -p.

However it is --preserve-merges.

Have you ever did a rebase assuming you would still have the merge commits? however rebase removed them.

Using -p / --preserve-merges you preserve the merges.

Note

I do not know how GitHub reacts with rewriting the merges (e.g. would the pull request re-open? I currently have no idea).