Option a is the correct answer. The Sufi work "Kashf-ul-Mahjub" was written by Abul Hasan al Hujwiri. Also known as Ali Hujwiri, he was a Persian Sufi saint and writer who lived in the 11th century. "Kashf-ul-Mahjub" is one of his most famous works and is considered a significant text in Sufi literature. It explores various aspects of Sufism, including spiritual purification, the stages of the Sufi path, and the concept of unveiling or "kashf."