الأدلة الشرعية أربعة: الكتاب والسنة والإجماع والقياس
The four principal sources of legal proof are the Book, Sunnah, consensus and analogy.
The Book refers to the Qurʾān. Sunnah includes authoritative Prophetic words, acts and approvals. Ijmāʿ is the agreement of qualified jurists on a legal question under the conditions recognized in legal theory. Qiyās extends an established ruling to a new case because the two share a legally relevant effective cause.
Listing the four is only a starting point. Each has questions of establishment, meaning and application. Consensus must not be confused with popularity, nor analogy with any loose resemblance. Their precise evidentiary conditions are discussed within the relevant juristic tradition.