In Chapter 15 Rambam explains how Aristotle never proved that the universe was eternal, so creation ex nihilo is at least possible. In 16 he says that as long as creation is possible, one can believe the prophets.

Guide For the Perplexed - Lecture 65: Part 2 Chapter 17

Join us as we study the monumental work of Maimonides, The Guide of the Perplexed. Let Maimonides speak to us in a language that we can understand, about issues that continue to perplex us in the 21st century. Learn how to approach those difficult times when what we believe seems to conflict with what the Holy writings say.