Here's the source:
http://theverge.com/2012/10/31/3579564/asus-google-nexus-7-sales-one-million-david-chang
My prediction threads:
Wii U will sell under 40m units (made on 14th September 2012)
PS Vita will sell under 20m units (made on 30th September 2012)
Wii U will sell under 7m in 2013 - I was right