In a religious legal system, the primary sources are the word of God and how the prophet(s) brought this into practice via their words, deeds etc.
The Sunna and Hadith (sayings/teaching/practices/actions) are the legacy of the Prophet Muhammad. Hadith collections reflect the traditions of Sunni and Imami Shiʿite Islam.
Arabic is the liturgical language of Islam. Below are some works in English as starting points:
Islamic studies bibliography included in collection below offering "... peer-reviewed annotated bibliographies on the range of lived experiences and textual traditions of Muslims as they are articulated in various countries and regions throughout the world. Bibliographies are browseable by subject area and keyword searchable."