First of all, we have to recognize the fact that the beliefs and practices of Islam did not create complete unity among Muslims for any significant length of time. We know that, upon the death of the prophet Muhammad, Muslims disagreed on who should lead them. This disagreement led to the split between Shi’a and Sunni Islam, a split which continues to be relevant today. Therefore, we must be somewhat cautious about saying that Muslims experienced unity.
That said, we can say that there are aspects of Muslim belief and practice that did tend to unify the Muslim community. Perhaps the most important of these is the idea that there is only one God and that all Muslims are equal under that God. This idea encouraged many people who were of low status in Arabian society to become Muslims. It helped ensure that Muslims would identify and feel a connection with one another. This helped encourage a feeling of unity among Muslims. One aspect of Muslim practice that encouraged unity was the requirement that all Muslims pray at five specified times during the day. This requirement ensured that many Muslims would pray together in public at various times. By engaging in this ritual together, they were able to create more of a feeling of unity than might have been present if worship were private and/or less frequent. A final aspect of Muslim practice that promoted unity was the requirement that Muslims give alms or charity to those who were less fortunate. This requirement encouraged Muslims to feel compassionate to their coreligionists who were poor, weak, or defenseless. This made it more likely that Muslims of various social classes and statuses would identify with one another instead of feeling distinct and separate.
All of these beliefs and practices helped to make Muslims feel unified, but they did not create absolute unity among Muslims.