The Kitáb-i-Íqán was revealed by Bahá’u’lláh in 1861/62. It is second only to the Kitáb-i-Aqdas in terms of its importance to Bahá’ís. In the Kitáb-i-Íqán, Bahá’u’lláh explains the foundational Bahá’í principle of progressive revelation whereby the prophet founders of all the major world religions have been progressively sent by God to reveal His guidance and teachings needed to carry forward an ever advancing civilisation. The Kitáb-i-Íqán outlines the reality of the Oneness of Religion and the error of regarding any prophet or religion as superior to any other.