The Gravitational Time Delay, now known as the Shapiro Effect, was first predicted by Einstein. It is proven by measuring the time delay of radar and radio beams sent between Earth and Mars. As the beams pass closer and closer to the Sun, a delay in the transit time is measured. This delay is caused by the gravitational force of the Sun. This delay also causes a Doppler shift in the signal, which is equivalent to the redshift observed for distant galaxies.
This figure illustrates these experiments, originally conducted by Dr. Irwin Shapiro of MIT.