Ductory passage:
In the year 1852 Baha'u'llah lay wrapped in the gloom of the Siyah-Chál, the subterranean dungeon of Tihrán. The darkness, filth, and character of the prisoners made that prison one of the most abominable places to which a human being could be condemned. It was there, with His feet in stocks and His neck weighted with chains that He received the first intimations of His Divine Mission.
-Based on the Writings of Shoghi Effendi, Messages to America by Shoghi Effendi, page 99.
During the days I lay in the prison of Tihrán, though the galling weight of the chains and the stench-filled air allowed Me but little sleep, still in those infrequent moments of slumber I felt as if something flowed from the crown of My head over My breast, even as a mighty torrent that precipitateth itself upon the earth from the summit of a lofty mountain. Every limb of My body would, as a result, be set afire. At such moments My tongue recited what no man could bear to hear.
-Bahá'u'lláh, Epistle to the Son of the Wolf, page 22.