Abu Bakr Ahmad ibn Husayn Ibn 'Ali Ibn Moussa al-Khosrojerdi al-Bayhaqi, البيهقي also known as Imam Al-Bayhaqi was born 994 CE/384AH in the small town of Khusraugird near Sabzevar, then known as Bayhaq, in Khurasan. During his lifetime, he became a famous Sunnihadith expert, following the Shafi'i school in fiqh and the Ash'ari school of aqeedah.
Al-Bayhaqi was a scholar of fiqh, of the Shafi'i school of thought as well as hadith. He studied fiqh under Abu al-Fath Nasir ibn al-Husayn ibn Muhammad al-Naysaburi and others. He also studied hadith under Hakim al-Nishaburi and others, and was al-Nishaburi's foremost pupil. He died in 1066 CE.