“Surely when a man is painting a picture he ought not refuse to hear any man's opinion… Since men are able to form a true judgement as to the works of nature, how much more does it behoove us to admit that they are able to judge our faults. Therefore you should be desirous of hearing patiently the opinions of others, and consider and reflect carefully whether or no he who censures you has reason for his censure; and correct your work if you find that he is right, but if not, then let it seem that you have not understood him, or, in case he is a man whom you esteem, show him by argument why it is that he is mistaken.”

Speech to the Electors of Bristol (3 November 1774); reported in The Works of the Right Honorable Edmund Burke (1899), vol. 2, p. 95
Context: Certainly, Gentlemen, it ought to be the happiness and glory of a representative to live in the strictest union, the closest correspondence, and the most unreserved communication with his constituents. Their wishes ought to have great weight with him; their opinions high respect; their business unremitted attention. It is his duty to sacrifice his repose, his pleasure, his satisfactions, to theirs,—and above all, ever, and in all cases, to prefer their interest to his own.
But his unbiased opinion, his mature judgment, his enlightened conscience, he ought not to sacrifice to you, to any man, or to any set of men living. These he does not derive from your pleasure,—no, nor from the law and the Constitution. They are a trust from Providence, for the abuse of which he is deeply answerable. Your representative owes you, not his industry only, but his judgment; and he betrays instead of serving you if he sacrifices it to your opinion.

The Notebooks of Leonardo da Vinci (1883), XIX Philosophical Maxims. Morals. Polemics and Speculations.

Immortality
1870s, Society and Solitude (1870), Books, Letters and Social Aims http://www.rwe.org/comm/index.php?option=com_content&task=category&sectionid=5&id=74&Itemid=149 (1876)

Variant: Relationship Principle 10
You can tell how much someone respects you by how much he respects your opinion. If he doesn't respect your opinion, he won't respect you.
Source: Why Men Marry Bitches: A Woman's Guide to Winning Her Man's Heart

His noting in his dairy after his contesting election in 1886 page=10.
Narrow-majority’ and ‘Bow-and-agree’: Public Attitudes Towards the Elections of the First Asian MPs in Britain, Dadabhai Naoroji and Mancherjee Merwanjee Bhownaggree, 1885-1906

April 25, 1778, p. 403
Life of Samuel Johnson (1791), Vol III

Responding to a reporter asking whether or not he believed that other players merited salaries comparable to his own (i.e. $52,000 a year, as per Ruth's newly signed 1922 contract), as quoted in "Have to Get More of 'Em,' Says Babe Ruth When He Hears of the Income Tax," in The St. Louis Post-Dispatch (March 10, 1922)