It was Avatar who fought alongside my father against the first mutant attack.
5 seconds sound clip from the Wizards (1977) movie soundboard.
You can hear this line at 00:57:57.900 in the Blu-ray version of the movie.
Quote context
[...]
- Join us, old wizard. We desperately need you.
- Is this how you're repayin' me?
- Stand back. Avatar will not be touched.
- When our world was young, so was mighty Avatar.
- It was Avatar who fought alongside my father against the first mutant attack.
- So now we have our messiah back again. He's going to destroy his brother for us.
- With what? A woman-child, one elf and a moron robot.
- It's Blackwolf. He's trying to gain control.
[...]