We report the first direct measurement of decays of the Λ_{c}^{+} baryon involving the neutron. The analysis is performed using 567 pb^{-1} of e^{+}e^{-} collision data collected at sqrt[s]=4.599 GeV with the BESIII detector at the BEPCII collider. We observe the decay Λ_{c}^{+}→nK_{S}^{0}π^{+} and measure the absolute branching fraction to be B(Λ_{c}^{+}→nK_{S}^{0}π^{+})=[1.82±0.23(stat)±0.11(syst)]%. A comparison to B[Λ_{c}^{+}→p(K[over ¯]π)^{0}] provides an important test of isospin symmetry and final state interactions.