Never in the Tripitaka were records of three religions in a single union.
Such is in no way a Buddhist concept or advocacy. The said religions
pertain to Confucianism under Confucius, Taoism under Lao Zi, and
Buddhism under Sakyamuni. Three founders, three scriptures,
three doctrines.
A few common grounds, though: filial devotion and righteous commitments,
charitable giving and virtue accumulated. Confucianism
teaches practice here and now; Taoism teaches the sweeping grand
theme of purity and nonaction; Buddhism teaches breakthrough in the
transmigration between rebirths and redeaths by way of a perfected
character manifest.
Union of the three religions is vaunting grandeur. It never took place.
On some verifications