Saudi security forces on Monday stormed the house of preacher, Salman Al-Ouda, who has been detained since 10 September.
Salman's son, Abdullah, said on his official Twitter account that security forces entered the house without a court order or legal procedures.
The officers searched his father's office and took two books from Abdullah's library because "they believed it to be my father's library".
The Saudi authorities have been cracking down on clerics, intellectuals and activists. Human Rights Watch described the campaign of arrests as part of ongoing human rights abuses in the country.
About a month and a half after Al-Ouda was arrested, Saudi authorities prevented his children from leaving the Kingdom.
Al-Ouda was arrested on 10 September and his brother, Khaled, was detained not long after.