This was written by a relative of mine, Ahn Jung-Geun
Thorns will grow in your mouth if you go one day without reading/studying.
(하루라도 책을 읽지 않으면 입속에 가시가 돋는다)
庚戌三月 扵旅順獄中 大韓國人 安重根 書
Third month of 庚戌 (1910), Imprisoned at Port Arthur, (written by) Ahn Jung-Geun, Citizen of the Korean Empire.