Plutarch, De Iside et Osiride
Goodwin, Ed.

Besides, Ptolemaeus Soter saw in a dream the colossus of Pluto that stood at Sinope (although he knew it not, nor had ever seen what shape it was of) calling upon him, and bidding him to convey it speedily away to Alexandria. And as he was ignorant and at a great loss where it should be found, and was telling his dream to his familiars, there was found by chance a certain fellow that had been a [p. 89] general rambler in all parts (his name was Sosibius), who affirmed he had seen at Sinope such a colossus as the king had dreamt of. He therefore sent Soteles and Bacchus thither, who in a long time and with much difficulty, and not without the special help of a Divine Providence, stole it away and brought it to Alexandria. When therefore it was conveyed thither and viewed, Timothy the expositor and Manetho the Sebennite, concluding from the Cerberus and serpent that stood by it that it must be the statue of Pluto, persuaded Ptolemy it could appertain to no other God but Serapis; for he had not this name when he came from thence, but after he was removed to Alexandria, he acquired the name of Serapis, which is the Egyptian for Pluto. And when Heraclitus the physiologist saith, Pluto and Bacchus are one and the same, in whose honor men are mad and rave, we are thus led to the same doctrine. For those that will needs have Pluto to be the body, the soul being as it were distracted and drunken in it, do in my opinion make use of an over fine and subtle allegory. It is therefore better to make Osiris to be the same with Bacchus, and Serapis again with Osiris, he obtaining that appellation since the change of his nature. For which reason Serapis is a common God to all, as they who participate of divine matters best understand.