Sunni Islam recognises six collections, the Kutub al-Sittah, all compiled in the ninth and early tenth centuries. Two stand above the rest, known jointly as the Sahihayn: the Sahih of al-Bukhari, who died in 870 CE, and that of Muslim ibn al-Hajjaj, who died in 875. Both selected a few thousand reports from far larger bodies of material they had collected, and Sunni consensus treats their contents as authentic, though individual reports have been challenged. The remaining four are the Sunan of Abu Dawud, who died in 888, al-Tirmidhi, 892, Ibn Majah, 887, and al-Nasai, 915. These are broader, arranged by legal topic, and include material their compilers themselves marked as weak. Earlier than any of them stands the Muwatta of Malik ibn Anas, a legal work built on Medinan practice.
Twelver Shia Islam has its own canon, the Four Books: al-Kafi of al-Kulayni, who died in 941; Man la yahduruhu al-Faqih of Ibn Babawayh, called al-Saduq, who died in 991; and Tahdhib al-Ahkam and al-Istibsar, both by al-Tusi, who died in 1067.
The two corpora differ because the criteria differ. Sunni hadith science holds the Companions of the Prophet collectively upright, so a Companion in a chain is not himself subject to criticism. Shia scholarship does not extend that presumption, holds a narrow set of early transmitters authoritative, and accepts as sound only chains running through the Imams of the Prophet's family, whose own sayings count as authoritative alongside the Prophet's. The result is not two versions of one collection but two largely separate bodies of material, with limited overlap and different authorities inside them.