Abu Dawud - Introduction
Imam Abu Dawud's collection is recognized by the overwhelming majority of the Muslim world to be one of the most authentic collections of the Sunnah of the Prophet (SAW), however it is also known to contain some weak ahadith (some of which he pointed out, others which he did not).
It is important to realize, however, that Imam Abu Dawud's collection is not complete: there are other scholars (i.e. Imam Bukhari, Muslim, Malik etc.) who worked as Imam Abu Dawud did and collected other reports.