Norton beat him in their first fight. Ali won a close decision. Some people said Norton Sr won the 3rd fight but the judges gave the decision to Ali.
This is partly why I consider Ali the most overrated fighter ever. Norton was nothing special, he's only known for scrambling Ali's brains. Yet Ali is widely considered the "GOAT" despite struggling with a guy who went on to have an unremarkable career.
If you fight frequently enough against top contenders and give them rematches you are more likely to suffer losses.
The once-a-year, "smart business decision" Americans of the modern age minimise that risk.
Ali also lost to Jimmy Young, but they gave the decision to him.