The translation is based on Athar-i-Qalam-i-Alá,Vol. 4, pp 258-267 and Risáli-yi-Tasbih-u-Tahlil, pp. 124-139. The two sources are cited below as "AQA" and "TT".
Documents posted between 2003-2012 had slightly different URLs and can be found in archive.org with addresses like bahai-library.com/?file=bahaullah_surah_pen.
Documents posted prior to October 2003 were at bahai-library.org [archive.org] and had completely different URLs.