In a statement that was read during a parliamentary session in Baghdad by his cousin, Liqaa al-Yassin, al-Sadr called the U.S. president the "greatest evil" for refusing to withdraw U.S. forces from Iraq.
"I address Bush, saying Iraqis from all walks of life have risen marching to the holy city of Najaf demanding [a U.S.] withdrawal. But you have not responded," al-Sadr's statement said.
"Your own people have been vociferous in demanding your withdrawal, but you have learned no lessons," the statement continued. "Indeed, the UN has appealed to you [saying] that you have no place as an occupier in Iraq. But you have not yielded. Now the Democrats are demanding that you withdraw, even if under a timetable. But you are adamantly [against] them."
The U.S. Congress has passed legislation that would require U.S. troops to begin leaving Iraq by October 1. Bush has said he will veto the measure.
The vote in the both the Senate and the House of Representatives fell far short of the two-thirds majority needed to overturn a presidential veto.
Al-Sadr led two armed uprisings against U.S. forces in 2004. His Imam al-Mahdi Army militia is thought to be responsible for sectarian killings in Iraq.
The U.S. military says al-Sadr has fled to Iran. But al-Sadr's followers insist that he is in Iraq.
(with material from agency reports)