Islam definitely does not teach that Mohammed was the greatest prophet, in fact Issa or Jesus as we call him is the prophet most praised and talked about in the Holy Koran, Mohammeds claim to fame is that he was the most recent prophet, at least to Muslims, and the last prophet, unless his message fails and a new one has to come. So Muslims would not say that Mohammed was greater than Abraham, or Moses, or Daniel, or David, in fact each prophet has their own distinct and unique contribution to make. No one looks at Mohammed as perfect or sinless, the way Christians look at Jesus, the main difference is that Muslims see Jesus as a prophet also, not God.