  Recent quasar absorption line observations suggest that reionization may end
as late as $z \approx 5.3$. As a means to search for large neutral hydrogen
islands at $z<6$, we revisit long dark gaps in the Ly$\beta$ forest in
VLT/X-Shooter and Keck/ESI quasar spectra. We stack the Ly$\alpha$ forest
corresponding to both edges of these Ly$\beta$ dark gaps and identify a damping
wing-like extended absorption profile. The average redshift of the stacked
forest is $z=5.8$. By comparing these observations with reionization
simulations, we infer that such a damping wing-like feature can be naturally
explained if these gaps are at least partially created by neutral islands.
Conversely, simulated dark gaps lacking neutral hydrogen struggle to replicate
the observed damping wing features. Furthermore, this damping wing-like profile
implies that the volume-averaged neutral hydrogen fraction must be $\langle
x_{\rm HI} \rangle \geq 6.1 \pm 3.9\%$ at $z = 5.8$. Our results offer robust
evidence that reionization extends below $z=6$.
