  We report the near-IR detection of a prominent CIV absorption in the
rest-frame UV spectrum of the most distant known QSO, SDSS J104433.04-012502.2,
at z=5.80. This QSO was recently observed with XMM-Newton and it was found to
be notably X-ray weak. The equivalent width of the CIV absorption feature (~10
A) strongly supports the idea that the X-ray faintness of this QSO is due to
heavy absorption by gas with a column density N_H > 10^{24} cm^-2. The shape of
the CIV feature suggests that this is a Broad Absorption Line QSO. Although
absorbed by a huge column of gas, the observed continuum in the 0.9-2.4um range
(~1300-3500 A rest frame) exactly matches the template of unabsorbed QSOs
without invoking any reddening (E(B-V)<0.08 mag), indicating that dust in the
absorbing gas is either absent or composed of large grains.
