Reality of Certainty (Arabic: Haqq al-Yaqeen) is a Shi'a Twelver hadith collection authored by the major Shia hadith scholar Allamah Mohammad Baqir Majlisi in the 16th century.[1]
It is a major secondary source of hadiths, which elaborates on hadith drawn from primary sources compiled centuries earlier such as al-Kafi and Man Yadhuru'l Faqih. Most of the primary Shia hadith collections are from the 10th and 11th centuries CE, and the secondary ones are either from the late Mongol era (14th century) or the Safavid era (16th-17th centuries).
Haqq al-Yaqeen has been criticized by some Shi'a in the words: Haqq al-Yaqeen has many weak narrators, none of the Hadith scholars have graded their narration as Sahih .
However, aside from the weak narrators, it also has many strong ones, and it is a well-researched book and contains more or less complete chains of narration, which many earlier books (including the Sunni collections of Bukhari and Muslim) tend to omit. From the Shia point of view, all hadiths books have at least a few weak narrators, since they were compiled by fallible people, therefore having weak narrators does not invalidate the whole book because hadiths are to be individually graded on their authenticity.
As proof, the narrators of the hadiths were obviously not the ones who got to decide what book they were placed in centuries later by scholars like Majlisi.