Source, in full
Correcting the Hansard proofs of his last speech to Parliament (31 March 1881), shortly before his death, cited in Harper's, Vol. 63 (1881). The quote is given in William Flavelle Monypenny and George Earle Buckle, The Life of Benjamin Disraeli, Earl of Beaconsfield, Vol. 1 (1929) as "I will not go down to posterity talking bad grammar".