新五代史
It was said that in his youth, Liu Xu was known for his handsome appearance and his literary abilities, and both his older brother Liu Xuan (rendered 劉晅 in the "History of the Five Dynasties" and 劉暄 in the "New History of the Five Dynasties") and younger brother Liu Hao () were known in their home territory. Sometime during the "Tianyou" era (904-907), there was a time when forces of the Khitan captured Zhuo, and Liu Xu was captured and taken to Xin Prefecture (新州, in modern Zhangjiakou, Hebei), but he escaped his Khitan captors. He later took up residence at Mount Daning (), living with Lü Mengqi () (later a Later Tang official as well) and Zhang Lin (), spending the time reciting and writing poems.