deskpro2k3 on 30 December 2016
other sources:
http://www.neogaf.com/forum/showthread.php?t=1328786
http://www.m-create.com/ranking/
According to pushsquare.com they got their source from the latest Media Create report.
"Japan's no longer the focus of Sony's attention, but the PlayStation 4 has still managed to quietly cross the four million units milestone in its home nation. The news comes courtesy of the latest Media Create report tracking sales for the week ending 25th December, where Sony's new-gen system sold 100,238 units – enough to push it past the aforementioned milestone."
