A person approached Imam ‘Ali (as) and confessed that he had committed a theft.
“Are you able to recite something from the Noble Qur’an?” Imam (as) asked him.
“Yes, I know the chapter al-Baqarah,” replied the man.
The Imam (as) said, “I forgive you because of the chapter al-Baqarah.” Ash’ath Ibn Qais, who happened to witness this, asked the Imam (as) whether he could repeal a punishment that had been stipulated by Allah.
“What do you know? If a person confesses to his crime, an Imam has the authority to either punish him or pardon him, but if two persons testify to a person’s crime, it is not permissible to annul the punishment (and pardon him),” the Imam (as) retorted.( Qadhawat-ha-e-Amirul Mo’minin, Page 119 (authored by Tustari) )