Regarding Lao-Tse: the Bahá'ís do not consider him a prophet, or even a secondary prophet or messenger, unlike Buddha or Zoroaster, both of Whom were divinely appointed and fully independent Manifestations of God.
As to the religion of the Sabaeans, very little is known about the origins of this religion, though we Bahá'ís are certain of one thing, that the founder of it has been a divinely-sent Messenger. The country where Sabaeanism became widespread and flourished was Chaldea, and Abraham is considered as having been a follower of that Faith. (From a letter written on behalf of Shoghi Effendi to individual believer, dated 10 November 1939; The Compilation of Compilations, vol. I, Extracts from the Baha’i Writings on Buddha, Krishna, Zoroaster, and related subjects)
