Abū Bakr Aḥmad ibn Ḥusayn Ibn ‘Alī ibn Mūsa al-Khosrojerdi al-Bayhaq also known as Imam Bayhaqi (rahimullah) 994 CE/384AH was born in the small town of Bayhaq, present day Khosrowjerd town in Iran.
Ahmad Shakir said in al-Ba’ith al-Hathith that Sunan- al – Kubra is the biggest book in legal hadiths. It has 21812 hadith or narrations. It includes most (if not all) of the hadiths found in al-Bukhari and Muslim, as well as many of those in Abu Dawud, al-Nasa’i, and al-Tirmidhi.
When reading the Sunan, it is important to note the following.
When Abu Abdullah, al-Hafiz is mentioned, it refers to Al-Hakim Nishapuri , the author of Mustadrak al-Hakim and the teacher of al-Bayhaqi.
Abu Bakr b. Ishaq refers to Ibn Khuzaymah.
Abu Ahmad refers to Ibn ‘Adi.
When ‘Ali or ‘Ali b. ‘Umar is mentioned it refers to al-Daraqutni.
These names are well-known luminaries of hadith criticism in the era after the compilers of the Six Books.