The Holy Spirit Itself hath been generated through the agency of a single letter revealed by Baha'u'llah

In the Súratu’l-Haykal, one of the most challenging works of Bahá’u’lláh, the following verses, each of which testifies to the resistless power infused into the Revelation proclaimed by its Author, have been recorded: “Naught is seen in My temple but the Temple of God, and in My beauty but His Beauty, and in My being but His Being, and in My self but His Self, and in My movement but His Movement, and in My acquiescence but His Acquiescence, and in My pen but His Pen, the Mighty, the All-Praised. There hath not been in My soul but the Truth, and in Myself naught could be seen but God.” “The Holy Spirit Itself hath been generated through the agency of a single letter revealed by this Most Great Spirit, if ye be of them that comprehend.”

-Shoghi Effendi

http://reference.bahai.org/en/t/se/WOB/wob-37.html