Hamza Kashgari fled Saudi Arabia for Malaysia in February last year after his tweets enraged some conservative Muslims and triggered death threats. He was extradited back to the kingdom days later and imprisoned.
"He was freed this morning," the 24-year-old's friend told Reuters, 20 months after the detention, but declined to comment further.
Prominent human rights lawyer Abdulrahman Allahim congratulated Kashgari on his release on Twitter.
Saudi Arabia's Justice Ministry was not immediately available for comment and there were no details on what led up to the release.
Kashgari, a former columnist in the kingdom's al-Bilad newspaper, had issued a long public apology after deleting the messages, and his family said he had repented. The authorities did not make any formal charges against him public.
Offences like blasphemy can be punished by death under the strict interpretation of Islamic law enforced in Saudi Arabia.
Kashgari's tweets addressed Prophet Mohammad (PBUH) on his birthday, saying he "loved the rebel in you" and "loved some aspects of you, hated others".
Saudi Arabia's Information Minister Abdul-Aziz Khoja said at the time the tweets had made him weep.
Raif Badawi, another blogger accused of blasphemy, is appealing against his sentence of seven years in prison and 600 lashes imposed this summer, his lawyer Waleed Abu al-Khair told Reuters.
Saudi Arabia also briefly released political rights activist Mohammed al-Bajadi this summer, but returned him to prison days after he was freed.
The kingdom has dismissed criticism of its human rights record from Western countries and campaign groups.
On Monday the cabinet issued a statement saying it "works to protect and promote human rights to maintain its identity, culture, gains and care for its citizens, on the basis of adherence to the Holy Quran".
A court in Kuwait on Monday upheld a 10-year prison sentence imposed on a man convicted of endangering state security by insulting Prophet Mohammad (PBUH) and the rulers of Saudi Arabia and Bahrain on social media.
Shia Muslim Hamad al-Naqi had denied the charges, saying his social media accounts had been hacked. New York-based Human Rights Watch on Tuesday called for him to be released.
"Ten years in prison for peaceful criticism shows just how little Kuwait respects freedom of expression," said the group's Joe Stork.
COMMENTS (7)
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@Jason Hollier: There was a facebook page by Saudis demanding his beheading which had more than 30,000 members.
@ET So you think you'll just take down the comment made by 'Concerned Man' and no one will notice. I have a screen shot saved of that. Something will happen because of that i assure you. You let that comment through.
If what they did was blasphemous i.e. proved by law that it was then shouldv'e been beheaded by now.'
@ Jason Hollier: This is the reason why word calls Pakistan as the epicenter of terrorism.
At least this man didn't get lynched or burnt by an enraged mob. That would've been his fate in your country.
Blasphemy is a vague charge meant to prop up weak foundations of dogma from discussion, criticism, and satire.
Saudi Arabia and these dogmatic middle eastern countries are the root of Muslim problems. And all Pakistan does is follow suit rather than create an original, south asian identity for itself rather than look to the Arabs for inspiration. Arabs, especially the Pharaonic Saudi Arabia, think that Islam is theirs to own and hence dominate the Islamic narrative in the world. Hypocrites they are and the true enemies of Pakistan.