Tensions between measured and predicted branching fractions of non-leptonic $B_{(s)}^0 \to D_{(s)}^{(\ast)-} h^+$ decays may be explained by the presence of new physics (NP) contributions capable of inducing $C\!P$ asymmetries up to O(1%).

The $C\!P$ asymmetry of flavour-specific $B_s^0 \to D_s^-\pi^+$ decays provides a clean test for NP.

This can be measured by the LHCb experiment as the flavour-untagged decay-time-integrated $C\!P$ asymmetry, $\langle A^s_{\rm untagged} \rangle$. 

This seminar presents the first measurement of $\langle A^s_{\rm untagged} \rangle$, performed using $5.4~{\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment between 2016 and 2018 at a centre-of-mass energy of $13~{\rm TeV}$.