LOUISVILLE, Ky. — Boxing champ Muhammad Ali is asking Iran to release two American hikers held since 2009 on spy charges.

Ali, arguably the most prominent U.S. Muslim, on Wednesday released a letter he wrote to supreme leader Ayatollah Ali Khamenei in February.

The letter asks Khameini to release Josh Fattal and Shane Bauer, who were arrested while hiking in northern Iraq near the Iranian border. A third hiker, Sarah Shourd, was released on bail in September, shortly after another letter Ali wrote to Khamenei.

Ali’s latest letter asks Khamenei as a brother in Islam to show the same mercy and compassion for the two men.