"Express your rejection by participating in this demonstration."
"Carry Iraqi flags that show the unity of Iraq."
"Do not ignore this protest as it is for the glory of Islam and victory of the grieving Iraqi people," the Shia leader said.
Iraq has remained tense since clashes erupted recently between security forces, backed by US troops, and al-Sadr's Mahdi Army.
Last week, the Mahdi Army fought fierce battles with the Iraqi security forces in the southern city of Basra and in Baghdad, after Nuri al-Maliki, the Iraqi prime minister, launched a crackdown on the outfit.
The fighting ended on Sunday after al-Sadr told his fighters to withdraw.
Earlier in 2004, al-Sadr had launched two fierce rebellions against the American military, before entering the political process.