E-Answer.Net

Exodus

Both of the above gave the correct answer, but remember that Moses' authorship of Exodus is based on tradition, not on scripture. In other words, we don't have any convincing evidence that it was Moses who wrote it, though it is safe to say that all of the accounts of Moses' life when he was alone must have come from him personally. Again, this does not prove that he wrote it, only that he spoke of these few private moments with the author or with someone who later related it to the author.

That would be Exodus.