idempotent completion

I would be grateful for getting the earliest reference to the fact that for two small categories T and S the corresponding functor-categories into Set are equivalent iff T and S have the same idempotent (= Cauchy) completion. One can find this in a russian paper: "Morita equivalent categories" by S. V. Polin, Vestnik Mosk. Univ., 1974, no.2, 41-45 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx alternative e-mail address (in case reply key does not work): J.Adamek@tu-bs.de xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx