I found this story on @HistoryWeird's blog here. The original source was a letter from M. Adlington, cited in Journal of the Royal Society of the Arts, v.57, October 1909.
"Natural historians have recorded several anecdotes about frogs and toads hibernating for prolonged periods, sometimes in confined or unlikely places. The early 19th century naturalist Dean Buckland reported a live frog being found in a block of freshly mined coal. Buckland tested amphibian hibernation with a series of experiments, entombing frogs in tree cavities and blocks of porous stone. Most of these proved unsuccessful and produced only dead and shrivelled up frogs and toads – however some of Buckland’s imprisoned subjects survived for up to two years. Another amazing account comes from a Mr Adlington of Jersey, who in 1856 found a large toad encased in the roots of palm tree:
"'The creature looked dead; the tree had ground round it… When [his gardener] began to cut the truck into sections he discovered the toad and split the tree in two to liberate it. The wood was simply rotten fibre, very white, and had evidently grown round the live creature, for when it came out of its hole, a perfect mound was left of it… Of course we thought it was dead and so buried it, but for fear it should come to life we poured boiling water on it. After about half an hour it showed signs of life. In about three days it began to swell out and get moist and hide under big leaves in the garden. In a month it was difficult to distinguish it from other toads, and it was very lively.'
"Adlington had sections of the tree examined by his local museum, which estimated that the toad had been buried for as long as 25 years. There is no mention in his report of the toad singing and dancing."