Wu Kuan (1435-1504), Letters. Photo: Sotheby's.

signed Qisheng Kuan, with one seal of the artist, yuan bo, and nine collectors' seals, ren qing, sun shi bo peng, hong, jian, qian, li du hu yin, cheng duan yun, wang yun lou zhen cang, zi hong jian shang; ink on paper, album leaves; each 25.7 by 13.3 cm. 10 1/8  by 5 1/4  in. (3). Estimation 20,000 -- 30,000 USD

Litterature: Calligraphy of Ming and Qing Masters, Vol. 1, Jiang Zhaoshen, Tokyo: Nigensha, 1987, pp. 8, 9, 26-31 

Sotheby's. Fine Classical Chinese Paintings & Calligraphy. New York | 19 sept. 2013 - http://www.sothebys.com