“It is thought that justice is equality, and so it is, though not for everybody but only for those who are equals; and it is thought that inequality is just, for so indeed it is, though not for everybody, but for those who are unequal.”

Expeditions of an Untimely Man, §48 Progress in my sense (Streifzüge eines Unzeitgemässen §48 Fortschritt in meinem Sinne). Chapter title also translated as: Skirmishes of an Untimely Man, Kaufmann/Hollingdale translation, and Raids of an Untimely Man, Richard Polt translation
Twilight of the Idols (1888)
Original: (de) Die Lehre von der Gleichheit! ... Aber es giebt gar kein giftigeres Gift: denn sie scheint von der Gerechtigkeit selbst gepredigt, während sie das Ende der Gerechtigkeit ist... "Den Gleichen Gleiches, den Ungleichen Ungleiches - das wäre die wahre Rede der Gerechtigkeit: und, was daraus folgt, Ungleiches niemals gleich machen."

Concurring, Dennis v. United States, 339 U.S. 162, 184 (1950).
Judicial opinions

Dissenting in New York v. United States, 331 U.S. 284, 353 (1947).
Judicial opinions

Whilst a paraphrase this is based off of Aristotle's writings as Aristotle stated "For instance, it is thought that justice is equality, and so it is, though not for everybody but only for those who are equals; and it is thought that inequality is just, for so indeed it is, though not for everybody, but for those who are unequal" in https://www.loebclassics.com/view/aristotle-politics/1932/pb_LCL264.211.xml Politics, III. V. 8.
Misattributed
This first appears in 1974 in an explanation of Aristotle's politics in Time magazine, before being condensed to an epigram as "Aristotle's Axiom" in Peter's People (1979) by Laurence J. Peter

2015, Remarks to the Kenyan People (July 2015)

Source: The Analects, Chapter VI

Source: Peter's People and Their Marvelous Ideas

Source: Wuthering Heights