The sunan genre differs from the jami by its focus. Where a comprehensive collection like al-Bukhari's ranges across belief, history and Quranic commentary, a sunan work confines itself to the traditions from which legal rulings are derived, ordered by the chapters of jurisprudence so that a working jurist can find the evidence for a question of ablution or inheritance where he expects it.
Abu Dawud's is the model of the genre. He reported that he had gathered half a million traditions and selected about 4,800 for the book, concentrating on reports that jurists had actually used, and he took a deliberately inclusive line at the margin: a tradition with a recognised weakness might still be recorded if nothing stronger existed on the point, because, as he explained, a weak tradition of the Prophet was dearer to him on a question of practice than the unsupported opinion of men. What keeps this from being laxity is his transparency. Throughout the book he appends brief verdicts, noting that a chain is broken, a transmitter contested or a wording anomalous, and where he is silent, he says in his letter to the Meccans, the tradition is at least serviceable. That letter, a short methodological treatise in its own right, survives and is studied as one of the earliest author's statements of editorial standards in the hadith literature.