Where To Look For An Answer If Controversial Religious Issues Arise?

Believers often engage in unjustified disputes on the topic of religion. They present arguments based on their own reflections on the verses of the Quran and the hadiths of the Prophet (peace be upon him). Where in such situations should believers look for a reliable answer to a controversial issue?
Based on the book by Abu Asad al-Hanafi «People of the Sunnah and Concord — who are they?»