They way my previous shop did this was to identify all tests that are needed for a story, be it new, regression, manual or automated, and created a test case for each one, and linked them to the overall task for that story.
That is one way, but only the way that made sense to us rather than a 'best practice'.
I would say the goal is to list all the activity you are doing for a sprint, and record progress against it. How you do that is up to you
We have multiple agile teams and the prevailing thought around regression testing is an activity sprint on its own.
We have 3-6 sprints where working functionality is delivered to QA in the sprint releases to work on automation of regression tests, and determination of the manual tests going forward.
After enough sprints are completed to provide enough business releasable functionality (due to impact to schedule around releases and not the functionality flushed out), it is sent to automation/regression teams for a sprint tracking around regression testing. This does not stop momentum in the main sprints as they can continue while a subset of the team, or a different team all together, performs the regression prior to release to production.
Its step by step after backlog i guess you get to learn,you can see it here and i guess you will be able to get the answer of your question.Because whenever i need some help regarding Scrum or Agile i approach this place.
In the best possible scenario, I mean for very mature teams, it is possible to end a Sprint (or finish with a set of functionality that makes sense to put it into production), just click a button and deploy to production. What does it take to get there? The most important thing is having an automated test suite running at all times (i.e. constantly doing regression testing). After all, as a developer, you need to be sure that, whenever you are modifying the codebase you are not breaking anything and get feedback about it as soon as possible. Most teams don't get there and the length of time you need for doing just regression testing defines how mature the team is and well it is working.
From my own experience, I have incorporated the regression testing effort for a user story into the story's testing tasks. I have kept these tasks up to date with the testing which will be/has been carried out.