Pope John XXIII
Mater et Magistra §126
Mater et Magistra: On Christianity and Social Progress
126 It seems to Us opportune to indicate certain directives that can contribute to a solution of this problem: directives which We believe have value whatever may be the historical environment in which one acts—on condition, obviously, that they be applied in the manner and to the degree allowed, suggested, or even demanded by the circumstances.
Source: Mater et Magistra (Vatican.va)