Strong gravitational lensing provides a powerful probe of the physical properties of quasars and their host galaxies .
A high fraction of the most luminous high-redshift quasars was predicted to be lensed due to magnification bias .
However , no multiple imaged quasar was found at z > 5 in previous surveys .
We report the discovery of J043947.08+163415.7 , a strongly lensed quasar at z = 6.51 , the first such object detected at the epoch of reionization , and the brightest quasar yet known at z > 5 .
High-resolution HST imaging reveals a multiple imaged system with a maximum image separation \theta \sim 0.2 \arcsec , best explained by a model of three quasar images lensed by a low luminosity galaxy at z \sim 0.7 , with a magnification factor of \sim 50 .
The existence of this source suggests that a significant population of strongly lensed , high redshift quasars could have been missed by previous surveys , as standard color selection techniques would fail when the quasar color is contaminated by the lensing galaxy .