200 FAQ On Muslims Belief by Hafiz Ibn Ahmed Al Hakami

A ---Yes, their call corresponded to each other, and their call was one and the same from the first among them till the last. They all invited men to the principle and essense of worship that is Tawhid (Monotheism or the Oneness of Allah the Almighty, which means, "none has the right to be worshipped except Allah the Almighty)." As for the religious rituals or duties, Prayers and Fasting for example might be ordained on some of them, while not on the others. Moreover, something might be made illegal for some of them while it is legal for the others by way of test and trial from Allah the Almighty: {That He might try you, which of you is the best in deeds}. (Hud, 7)