Parshat Ki Tisa
In 32:19 Moshe gets down the mountain and is shocked by what he sees.
Why is he shocked? Hashem told him what was going on..he already davened on their behalf, so why the surprise and anger?
Even though he had acted on the info on their behalf, he did not really believe it. he could not believe it. In a sense it was Lashon Ha'Ra. No matter how reliable the info, how reliable the source, you cannot accept Lashon Ha'Ra except "l'toeles".
Moshe had a "toeles" - he had to daven for them. So he accepted it for that much, so he could daven for them. But that is it. To actually believe it, which had no other toeles, he had to assume it was not so bad or there was a mistake or something.
therefore he was surprised when he actually saw what was going on.