It was extremely close - the day was July 12, 1916 at the Fort de Souville, in the morning.
Souville was the very last of the French fort to hold, behind was the top of the last hill, and on the other side was the town of Verdun itself.
The Germans were only a hundred meters from Souville, launched an attack, with the survivors actually reaching the top of the fort. There was little men standing, though - not more than a dozen. Those men stood there for what, 15 minutes ? and they could see the town of Verdun not that far away. Then the french got out of the fort and wiped them out.
Never did the Germans reached Souville again. Within days, the french counter attacked and pushed the frontline far enough from Souville. Whatever happened after that point, Verdun was a stalemate. I think it is more or less the moment when the Germans lost WWI - although that could be discussed of course.