Abusa'id Abolkhayr or Abū-Sa'īd Abul-Khayr (Persian: ابوسعید ابوالخیر) (December 7, 967 - January 12, 1049), also known as Sheikh Abusaeid or Abu Sa'eed, was a famous Persian Sufi and poet who contributed extensively to the evolution of Sufi tradition.The majority of what is known from his life comes from the book Asrar al-Tawhid (اسرارالتوحید, or "The Mysteries of Unification") written by Mohammad Ibn Monavvar, one of his grandsons, 130 years after his death.