Green’s Dictionary of Slang

arms of murphy n.

In phrases

in the arms of murphy [a pun on the classically based arms of Morpheus, the Greek god of sleep or dreams]

asleep.

1819		Fudger Fudged 40: A young Irish lady (not Miss Owenson) being surprised sleeping on a bank of shamrocks, sentimentally exclaimed — Ah ! you find me in the arms of Murphy.
1828		Night Watch 2 136: No featherbed was ever welcomer to me. I was fast locked in the arms of Murphy, as the scholars say.
1837		Gurwood (ed.) General Orders of Field Marshal the Duke of Wellington xxxiii: It is singular to refer to these orders to see how a division of 6000 men, [...] rolled up in their blankets ‘in the arms of Murphy,’ were all dressed, with blankets rolled, packed, equipped, squadded, paraded in companies [etc.].
1851		R.S. Surtees Young Tom Hall (1926) 321: Jug and Mrs Blunt were, as Mr Doiley sad, ‘in the arms of Murphy’.
1854		Bell’s Life in Sydney 2 Sept. 2/6: [She] found herself unable to find a lodging, and feeling anxious to get into the arms of ‘Murphy’, claimed the protection of the Charlies.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1873		Sl. Dict.
1922		Joyce Ulysses 614: Anyhow, they passed the sentrybox with stones, brazier, etc. where the municipal supernumerary, ex-Gumley, was still to all intents and purposes wrapped in the arms of Murphy, as the adage has it, dreaming of fresh fields and pastures new.