One question posed by Chung and Luh is answered. Namely, let R be a prime ring with center Z and d a non-zero derivation of R. Suppose xdn - xam ∈ Z for all x ∈ R, where n > m are fixed non-negative integers. Then R is commutative if any one of the following conditions is satisfied: (I) m = 0;(ii) m = 1, n > 1 an even integer, and charR ≠ 2; (iii) m = 2, n > 2 an odd integer, and char R ≠ 2.