Together Qur'an and Sunnah constitute the two sources of the law (Shari'ah) of God, a guide to prosperity and happiness in this life and to the bliss of the hereafter.
One of the first books of jurisprudence taught to students is the Waraqat of Imam al-Juwayni, often with a short commentary by Jalal al-Din al-Mahalli.
How is one to wade through the apparent welter of irreconcilable primary Islamic sources? What is one to do when faced with opposing practices of the Prophet (Sallallahu Alayhi Wa Sallam) on the same issue? When is a practice deemed necessary or recommended? These are some of the topics discussed in usul al-fiqh.