How many structures remain in mecca that date back to the time of Muhammad ?
These include the mosque originally built by Muhammad 's daughter Fatima , and other mosques founded by Abu Bakr ( Muhammad 's father - in - law and the first Caliph ) , Umar ( the second Caliph ) , Ali ( Muhammad 's son - in - law and the fourth Caliph ) , and Salman al - Farsi ( another of Muhammad 's companions ) .