  The internal structure of the charm-strange mesons $D_{s0}^*(2317)$ and
$D_{s1}(2460)$ are subject of intensive studies. Their widths are small because
they decay dominantly through isospin-breaking hadronic channels
$D_{s0}^*(2317)^+\to D_s^+\pi^0$ and $D_{s1}(2460)^+\to D_s^{*+}\pi^0$. The
$D_{s1}(2460)$ can also decay into the hadronic final states $D_s^+\pi\pi$,
conserving isospin. In that case there is, however, a strong suppression from
phase space. We study the transition $D_{s1}(2460)^+\to D_s^+\pi^+\pi^-$ in the
scenario that the $D_{s1}(2460)$ is a $D^*K$ hadronic molecule. The $\pi\pi$
final state interaction is taken into account through dispersion relations. We
find that the ratio of the partial widths of the $\Gamma(D_{s1}(2460)^+\to
D_s^+\pi^+\pi^-)/\Gamma(D_{s1}(2460)^+\to D_s^{*+}\pi^0)$ obtained in the
molecular picture is consistent with the existing experimental measurement.
More interestingly, we demonstrate that the $\pi^+\pi^-$ invariant mass
distribution shows a double bump structure, which can be used to disentangle
the hadronic molecular picture from the compact state picture for the
$D_{s1}(2460)^+$. Predictions on the $B_{s1}^0\to B_s^0\pi^+\pi^-$ are also
made.
