If the OED has "benefit of clergy", then why not ...

[Joel S. Berson]

"benefit-of-linen"?

Hoffer, Peter C. and N. E. H. Hull, _Murdering Mothers: Infanticide
in England and New England 1558--1803_ (New York: New York University
Press, 1981), pp. [68--]69.

"On December 17, 1673, Ann Jewring pleaded her innocence of
infanticide using evidence that she had made linen for her infant
before its birth. She was a single woman and had concealed her
pregnancy, the delivery of the child, and its death. The [69] corpse
was discovered hidden in a box, but the coroner's jury did not charge
her with the crime. In effect, she had pleaded a benefit-of-linen
against the letter of the statute [21 James I, c. 27, which made a
finding of concealment sufficient for conviction as a capital crime].
There is no way of knowing how popular or effective this line of
defense was before 1700, but after that date, benefit-of-linen, in
the absence of evidence of violence upon the corpse, almost
guaranteed an eventual acquittal in newborn bastard death trials. ...
In 1718 ... there were six cases of infanticide [recorded in the Old
Bailey Sessions Papers]. In five of these, the mothers of dead
newborn bastards pleaded benefit-of-linen, and all were acquitted.
The reporter noted when defendants had linen, and the linen was
brought into court."

This may be a coining; I did not find any earlier instance in
GBooks.  (There are later uses, through 2012.)  However, a footnote
in _Manifest Madness_ (2012), p. 209, n. 21, cites R. W. Malcolmson,
"Infanticide in the Eighteenth Century", in J. S. Cockburn, ed.,
_Crime in England 1550--1800_ (London: Methuen, 1977), p. 198.  I do
not know if Malcolmson actually uses the phrase (GBooks provides only Snippte).

If the phrase was actually used in the 17th or 18th centuries, some
places to look would be the Old Bailey Sessions Papers,  17th and
18th Century Burney Newspapers, and British Periodicals.  My quick
search in the OBSP yielded no results.

Joel

------------------------------------------------------------
The American Dialect Society - http://www.americandialect.org