Race stewards revealed three hours after the race and the ruling does not affect Rosberg's standings.
The ruling and the punishment in fact meant that Rosberg kept fourth place in the race result, and his lead of 11 points in the drivers' world championship.
The stewards said: "Having taken note of the extensive evidence given by both drivers and the video and telemetry data, it was apparent that Car 44 (HAM) was in front of Car 6 (ROS) - i.e. more than fully alongside - and that the driver of Car 44 could have clearly made the turn (T2) on the track, if not for the resultant collision.
"Car 6 did not allow Car 44 "racing room" and hence the driver of Car 6 was responsible for the collision."
The championship leader was also awarded two penalty points for the accident and a reprimand for not having stopped while his car was damaged.
"We do note the extenuating circumstances and the fact that the driver of Car 6 (ROS) did slow down significantly and attempted to mitigate the risk to other drivers and cars," the stewards added.