The first study of Formula omitted violation in the decay mode Formula omitted, with Formula omitted, is presented, exploiting a data sample of proton-proton collisions collected by the LHCb experiment that corresponds to an integrated luminosity of Formula omitted. The analysis is performed in bins of phase space, which are optimised for sensitivity to local Formula omitted asymmetries. Formula omitted-violating observables that are sensitive to the angle Formula omitted of the Unitarity Triangle are determined. The analysis requires external information on charm-decay parameters, which are currently taken from an amplitude analysis of LHCb data, but can be updated in the future when direct measurements become available. Measurements are also performed of phase-space integrated observables for Formula omitted and Formula omitted decays.