You can not Scrum without XP practices, especially Continuous Integration

When I started my first Scrum project back in 2008, I am not very familiar with Continuous Integration (CI). After all, CI belongs to Extreme Programming and not Scrum, it was not being introduced to me properly during my Certified Scrum Master course.

When I got back to office and start implementing Scrum process, I hence overlook the important of CI. It went pretty well for me with the product backlog, sprint planning session, daily scrum, sprint review session and retrospective. The team and company enjoy tremendous benefits from those activities. We have a sprint before each release to perform hardening (more throughout testing and etc).

I realize something is wrong during the first sprint after the first release, the team's velocity is getting slower and slower, QA need more and more time to complete their testing. Items in the product backlog has become harder and harder to implement. It reaches a point where it almost halts the entire project.

It was not clear to me what went wrong, how would such a great framework turn out to be like chewing gum? It was sweet in the beginning but soon turn bitter. I only come to conclusion and the answer when I come across the topic of CI later on. My question is, why is CI not being emphasized in the Scrum course? I would expect the Agile community practice what they peach for on the transparency, trust, honesty. So Scrum courses should introduce and emphasize the important of CI, even though it is "invented" by other Agilists.