釋氏要覽 1.157

1.157

蓋寺院之正寢也。始因唐顯慶年中勅差衛尉寺承李義表前融州黃水令王玄策往西域充使。至毘耶黎城。東北四里許。維摩居士宅示疾之室。遺址疊石為之。王策躬以手板縱橫量之得十笏。故號方丈。

This is the principal dwelling chamber of a monastery. It originally began in the Xianqing era of the Tang dynasty, when an imperial decree dispatched Li Yibiao, Administrator of the Court of the Imperial Insignia, and Wang Xuance, former Magistrate of Huangshui in Rongzhou, on a diplomatic mission to the Western Regions. When they arrived about four li northeast of the city of Vaiśālī at the room where the layman Vimalakīrti manifested illness, its ruins were made of piled stones. Wang Xuance personally measured it both lengthwise and crosswise with his writing tablet, finding it to be ten tablets [on each side]. Hence it was designated the "Ten-Foot Square" (Fangzhang).