Kitab Al-Iman - Al-Imam al-Qasim ibn Salaam (224H)

This book is among the first risala written by an imam from the Salaf defining belief of the people of the Sunnah and refuting the people of innovation: This is Kitab al-Iman, of Imam Abi 'Ubayd, al -Qasim ibn Sallam (157-224H).