Sanhedrin 100 - The Book of Ben Sira
Rabbi Yochanan expounded: " In the future the Holy One Blessed is He will bring precious stones and pearls that are thirty by thirty amot, will cut out from them openings that are twenty by ten, and will install them to be the gates of Jerusalem. " One student mocked him, but once, at sea, this student saw ministering angels who were sawing precious stones and pearls as Rabbi Yochanan had described. Upon return, he told Rabbi Yochanan, "Keep expounding, for I saw such stones!" Rabbi Yochanan replied, "And if you have not seen it, you would not have believed it?!" set his eyes on the student, and he turned into a heap of bones.
One who reads "external books" may loose his share in the World to Come. Some say, these are all books not Torah-related, but others say, these are only heretical books, but writings such as Homer's are permitted.
There is a similar disagreement about the Book of Ben Sira. Ben Sira was a son of the prophet Jeremiah. Rav Yosef quoted him, "A beautiful wife - fortunate is her husband, the number of his days is doubled" (or at least it seems to him so).
Art: Jan Frederik Pieter Portielje - The Jewel Case