Observation of the decay $D_s^{+}\to \omega {\pi }^{+}\eta$

Using 7.33 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data collected by the BESIII detector at center-of-mass energies between 4.128 and 4.226~GeV, we observe for the first time the decay $D_s^{\pm }\to \omega {\pi }^{\pm }\eta$ with a statistical significance of 7.6$\sigma$. The measured branching fraction of this decay is $(0.54\pm 0.12\pm 0.04)\mathrm{\%}$, where the first uncertainty is statistical and the second is systematic.