  Hot subdwarf B stars (sdBs) are core helium-burning stars located on the
extreme horizontal branch. About half of the known sdB stars are found in close
binaries. Their short orbital periods of 1.2 h to a few days suggest that they
are post common-envelope systems. Eclipsing hot subdwarf binaries are rare, but
important to determine the fundamental stellar parameters. Low-mass companions
are identified by the reflection effect. In most cases the companion is a main
sequence star near the stellar mass limit. Here we report the discovery of an
eclipsing hot subdwarf binary SDSS J162256.66+473051.1 (J1622) of very short
orbital period (0.0697 d), found in the course of the MUCHFUSS project. The
lightcurve shows grazing eclipses and a prominent reflection effect. An
analysis of the light- and radial velocity (RV) curves indicated a mass ratio
of $q=$ 0.1325, an RV semiamplitude $K=47.2\rm\,km\,s^{-1}$, and an inclination
of $i=72.33^\circ$. We show that a companion mass of 0.064 $M_{\rm \odot}$,
well below the hydrogen-burning limit, is the most plausible solution, which
implies a mass close to the canonical mass (0.47 $M_{\rm \odot}$) of the sdB
star. Therefore, the companion is a brown dwarf, which not only survived the
engulfment by the red-giant envelope, but also triggered its ejection, and
enabled the sdB star to form. The rotation of J1622 is expected to be tidally
locked to the orbit. However, J1622 rotates too slowly ($v_{\rm rot}=74.5\pm
7\rm\,km\,s^{-1}$) to be synchronized, challenging tidal interaction models.
