Mathematics - There is a tradition in mathematics that says "Read the Masters!" Thanks to the Mathematical Association of America, this is now easier: gathered in one place are masterful expositions of mathematics, from 1925 to the present, written by winners of the Chauvenet Prize.
Where "Read the Masters!" originated:
"Euler learned at the feet of Johann Bernoulli, who had Euler 'read the masters'. Euler read difficult mathematics and Bernoulli helped him when he got stuck. In his later years, I propose that Euler was able to teach in the style under which he himself had learned. He had learned guided by the principle 'Read the masters'. He taught under the style 'Read me, read me. I am Euler and I am your teacher in all things.' (Edward Sandifer, How Euler Did It, Euler as a Teacher, Part 2, Feb 2010)
Laplace on Euler (1749-1827): "Read Euler, read Euler. He is the master of us all." (quoted as a personal communication by Gugliemo Libri, Journal des Savants, p.51, 1846)
Neils Abel (1826), when asked how he got his expertise, replied, "It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils." (Letter to Bernt Holmboe, quoted by Oystein Ore, Abel: Mathematician Extraordinaire, 1957)
References:
[1] The Chauvenet Prize Archive
http://www.maa.org/programs/maa-awards/writing-awards/chauvenet-prizes
[2] Edward Sandifer: Euler as Teacher, part 2:
http://eulerarchive.maa.org/hedi/HEDI-2010-02.pdf
Full Archive: http://eulerarchive.maa.org/hedi/
[3] Euler biography, and Laplace's quote:
https://plus.maths.org/content/os/issue42/features/wilson/index
https://en.wikipedia.org/wiki/Leonhard_Euler
[4] Neils Abel, his student years:
https://en.wikipedia.org/wiki/Niels_Henrik_Abel#Cathedral_School_and_Royal_Frederick_University