Muhammad Ali, the 73-year-old three-time world heavyweight champion, spoke out against Donald Trump’s proposal to ban Muslims from entering the U.S.

He aimed his statements at “presidential candidates proposing to ban Muslim immigration to the United States,” but the clear target is Trump, who hasn’t backed down after making a proposal to ban any Muslim from entering the U.S. after the deadly shootings in San Bernadino, Calif.

Ali calls for all Muslims to “stand up to those who use Islam to advance their own personal agenda.” He notes that “They have alienated many from learning about Islam.”

Prominent public figures, including Facebook creator and CEO Mark Zuckerburg, have spoken out in support of Muslims in response to Trump’s harmful proposals.

In his national address this past Sunday, President Barack Obama called for Americans to “reject discrimination.”

Obama also reminded the nation that Muslim Americans are “our friends, neighbors, coworkers and sports heroes.” Muhammad Ali is one of the most popular Muslim figures in American sports culture.

Trump made a dig toward Ali with this Tweet:

Trump has met Ali on multiple occasions and, according to BBC, received an award named after the former heavyweight champion in 2007.

“True Muslims know that the ruthless violence of so called Islamic Jihadists goes against the very tenets of our religion… these misguided murderers have perverted people’s views on what Islam really is.” — Muhammad ali