The totally asymmetric simple exclusion process (TASEP) on the
one-dimensional lattice with the Bernoulli \rho measure as initial conditions,
0<\rho<1, is stationary in space and time. Let N_t(j) be the number of
particles which have crossed the bond from j to j+1 during the time span [0,t].
For j=(1-2\rho)t+2w(\rho(1-\rho))^{1/3} t^{2/3} we prove that the fluctuations
of N_t(j) for large t are of order t^{1/3} and we determine the limiting
distribution function F_w(s), which is a generalization of the GUE Tracy-Widom
distribution. The family F_w(s) of distribution functions have been obtained
before by Baik and Rains in the context of the PNG model with boundary sources,
which requires the asymptotics of a Riemann-Hilbert problem. In our work we
arrive at F_w(s) through the asymptotics of a Fredholm determinant. F_w(s) is
simply related to the scaling function for the space-time covariance of the
stationary TASEP, equivalently to the asymptotic transition probability of a
single second class particle.