  From samples of $pp$ collision data collected by the LHCb experiment at
$\sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0,
2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $\Lambda_b^0K^-$ and
$\Xi_b^0\pi^-$ invariant mass spectra is observed. In the quark model, radially
and orbitally excited $\Xi_b^-$ resonances with quark content $bds$ are
expected. Referring to this peak as $\Xi_b(6227)^-$, the mass and natural width
are measured to be $m_{\Xi_{b}(6227)^-}=6226.9\pm2.0\pm0.3\pm0.2$ MeV/$c^2$ and
$\Gamma_{\Xi_b(6227)^-}=18.1\pm5.4\pm1.8$ MeV/$c^2$, where the first
uncertainty is statistical, the second is systematic, and the third, on
$m_{\Xi_b(6227)^-}$, is due to the knowledge of the $\Lambda_b^0$ baryon mass.
Relative production rates of the ${\Xi_b(6227)^-\to\Lambda_b^0K^-}$ and
${\Xi_b(6227)^-\to\Xi_b^0\pi^-}$ decays are also reported.
