The surviving members of Stalin’s staff in recent years say the opposite — that Stalin couldn’t believe the reports of the attacks, and took a great deal of convincing that Hitler had attacked. The most surprising part of this, IMHO, is that any of Stalin’s staff *survived* Stalin. ;’)
On the German side, in the book “Interrogations”, a high-ranking German general, captured and interrogated, told his Allied inquisitor that Hitler was constantly concerned about the reports of Soviet raids across the frontier after the division of Poland.
Whoops... (add in where needed) and Stalin couldn’t believe Hitler would break the treaty.