Mustafa Sönmez, a Turkish professor and a columnist, has been detained by Turkish police for “insulting” Turkish President Recep Tayyip Erdogan on social media.

He released on Sunday after testifying to a prosecutor. According to the Cumhuriyet daily, Sönmez was questioned about his Twitter posts that are in critical of the Turkish government and President Erdogan.

After being released late on Sunday, Sönmez tweeted that he has been detained by police six times in the past for insulting Erdogan and his son Bilal.