Possible Clues:

• You'd sound ravin' to quote thus, but not ever again
• When pigs fly, as the raven put it
• Not a gain ever? Sounds as if you're ravin'
• Raven's word
• Tyneside vicar backing humanist? Not again, not at any time!
• Constant or fading corvine cry?
• Old-fashioned 'That's absolutely the last time'
• Final word of "The Raven"
• Uniform returned by marines, nothing by engineers -- not again!
• The sort of a quotation you would not get in future from a blackbird?