Let Γ be a nonelementary discrete subgroup of SU(n, 1) or Sp(n, 1). We show that if the trace field of Γ is contained in R, Γ preserves a totally geodesic submanifold of constant negative sectional curvature. Furthermore if Γ is irreducible, Γ is a Zariski dense irreducible discrete subgroup of SO(n, 1) up to conjugation. This is an analog of a