As quoted in Genetic Studies in Joyce (1995) by David Hayman and Sam Slote. Though such remarks have often been quoted as Wellington's response on being called Irish, the earliest published sources yet found for similar comments are those about him attributed to an Irish politician:
The poor old Duke! what shall I say of him? To be sure he was born in Ireland, but being born in a stable does not make a man a horse.
Daniel O'Connell, in a speech (16 October 1843), as quoted in Shaw's Authenticated Report of the Irish State Trials (1844), p. 93 http://books.google.com/books?id=dpKbWonMghwC&pg=PA93&dq=%22+make+a+man+a+horse%22&num=100&ei=0YVZSIWXCIiSjgG37bGIDA
No, he is not an Irishman. He was born in Ireland; but being born in a stable does not make a man a horse.
Daniel O'Connell during a speech (16 October 1843), as quoted in Reports of State Trials: New Series Volume V, 1843 to 1844 (1893) "The Queen Against O'Connell and Others", p. 206 http://books.google.com/books?id=zWETAAAAYAAJ&pg=PT108&dq=%22+make+a+man+a+horse%22&num=100&ei=MohZSJ-PK4a4jgG-lLGJDA
Variants: If a man be born in a stable, that does not make him a horse.
Quoted as as an anonymous proverb in Dictionary of Quotations from Ancient and Modern English and Foreign Sources (1899), p. 171
Because a man is born in a stable that does not make him a horse.
Quoted as a dubious statement perhaps made early in his career in The Concise Oxford Dictionary of Proverbs (1992) edited by John Simpson and Jennifer Speake, p. 162.
Misattributed
