In “History in Quotations”, which reflects five thousand years of World History, the authors M. J. Cohen and John Major write as follows: 

“Muhammad said: 

‘He of whom I am the Mawla (patron), Ali is his Mawla. O God, be the friend of him who is his friend and be the enemy of his enemy.’ 

This became the proof text for the Shia claim that Ali, the Prophet’s cousin and son-in-law, was the Prophet’s rightful successor after the Prophet’s death in 632. The meaning of Mawla here probably implies the role of patron, lord or protector.” 

The authors sum up by stating that through the use of the term Mawla, Muhammad was giving Ali the parity with himself in this function.