The petition was sent to Musharraf last week both by post and through the high-security jail near Lahore, where Singh is currently imprisoned, seeking pardon under the powers granted to the President by Pakistan's constitution, the Indian prisoner's lawyer, Rana Abdul Hameed, told PTI on Saturday.
Hamid, who has been hired by a Canadian human rights group to defend Singh, said from Lahore over phone that the mercy petition was filed after the Supreme Court last month dismissed an application by him seeking a review of the death sentence given to him in a bomb blast case at Yakkin Gate in Lahore in 1990 in which three persons were killed and several injured.
The mercy petition was filed even though the Supreme Court is yet to give its verdict on another case against Singh in which he was accused of committing three more bomb blasts in Pakistan's Punjab province.
In all 14 people were killed in the four bomb blasts in which Singh was accused of involvement by Pakistan police, who alleged that he was an Indian spy and entered Pakistan through the Punjab border to cause sabotage.
The mercy petition in Yakkin gate case has been filed to prevent the Pakistani authorities from acting on his death sentence even though one more case was pending against him in connection with the three bomb blasts.
In his earlier petitions to the courts, including the Supreme Court, Singh said he inadvertently crossed the border and later caught by police and wrongly implicated in the cases.
Hamid said that in the mercy petition, it has been argued that Singh, who Pakistan police claimed is Manjit Singh, was not given a proper opportunity to defend himself both in the anti-terrorism court and later in the higher courts.
Seeking the pardon, the mercy petition argued that Islam has a provision to pardon a non-Muslim. "Islam is a vast religion and it has grace to pardon non-Muslim. The man who pardons is regarded as a great person under the religion," Hamid said.
The petition also sought Sarabjit Singh's release for the betterment of India-Pakistan relations, which have vastly improved during the past three years. "If Sarabjit Singh is not pardoned it could have adverse impact on the relations between the two countries," Hamid said.
He said he has stated in the petition, "Sarabjit Singh should be pardoned in the interest of improving relations between the two countries."
Musharraf is expected to act on the petition after the Supreme Court delivers a judgement on Singh's another review petition involving three bomb blast cases in Punjab province.