Saudi Arabia has released prominent novelist Turki al-Hamad, who was arrested in December after a series of tweets criticising Islamism and saying Islam needed renewal, an activist said.
"He is in his house now in Riyadh," said Waleed Abu al-Khair, a lawyer and human rights activist in the conservative Islamic kingdom, where criticism of the Muslim faith, or senior members of the clergy and ruling family, is not tolerated.
Hamad, one of Saudi Arabia's best known liberal thinkers, was not tried during his six months in jail, Abu al-Khair said on Wednesday.
Before his detention he wrote tweets that likened some ultra-conservatives to Nazis and called for a renewal of Islam.
The Justice Ministry was not immediately able to comment on Hamad's release or the reasons for his detention. Hamad's mobile telephone remained switched off on Wednesday.
Last year, Saudi Arabia imprisoned a young blogger, Hamza Kashgari, on blasphemy charges after he published tweets that imagined a conversation with the Prophet Muhammad. Kashgari remains behind bars.
Saudi Arabia, the birthplace of Islam and home to the faith's holiest sites in Mecca and Medina, practises Islamic law, allowing judges to pass verdicts and sentences based on their interpretation of religious and legal texts.
Blasphemy is illegal, as is leaving the Islamic faith.
Morality police patrol public areas to ensure that strict religious norms, including modest dress, are observed, while the public practice of other religions is forbidden.