  Using a data sample corresponding to an integrated luminosity of 0.35
$\mathrm{fb}^{-1}$ collected by LHCb in 2011, we report the first evidence of
CP violation in the decays of $B^0_s$ mesons to $K^\pm \pi^\mp$ pairs,
$A_{CP}(B^0_s \rightarrow K \pi)=0.27 \pm 0.08\,\mathrm{(stat)} \pm
0.02\,\mathrm{(syst)}$, with a significance of 3.3$\sigma$. Furthermore, we
report the first observation of CP violation in $B^0$ decays at a hadron
collider, $A_{CP}(B^0 \rightarrow K\pi)=-0.088 \pm 0.011\,\mathrm{(stat)} \pm
0.008\,\mathrm{(syst)}$, with a significance exceeding 6$\sigma$.
