Of course they provide source! Source rpms and tgz are downloadable.

Enterprise isn’t gpl, but source is provided.

(This could have been easily answered with a google search, as you pointed out)

No, I meant that I did search it on Google, and couldn't easily see from the results which case it is. Google "mongodb enterprise source code" -- which one answers the question?

If it were so easy, you could have provided the citation yourself in that comment.