Verily I say unto you, this generation shall not pass away till all be fulfilled.

Heaven and earth shall pass away, but my words shall not pass away." Such is the prophecy, and on it I would remark, first, that what Jesus here foretells concerning Jerusalem did in fact come to pass.
But that was not a fulfillment of his prophecy, but of Daniel's, who did, as is set down in the 7th chapter of this work, expressly foretell the utter destruction of the city and the temple.

And it was from Daniel that Jesus obtained his know-ledge of the approach of that event.

For he expressly cites Daniel, Matthew xxiv.

15; Mark xiii.