They all gave the same basic teaching: that man should worship God, and God alone, and do good to his fellow beings. Ofcourse, the details of the teachings differed according to the nation and the time in which a Prophet appeared. In the Quran, the teachings of all Prophets are called Islam, and the Prophets and their true followers are labelled Muslims. This refers to the fact that the fundamental teachings given by all of them were the same - submission to God.