New Defender's Study Bible Notes
8:6 wrote on the ground. The only other recorded instance of God writing “with His finger” is when God wrote the ten commandments on two slabs of stone (Exodus 31:18). It would have been profoundly significant, as well as profoundly stirring and convicting, to the woman’s accusers, if Jesus also was seen writing out these commandments instead of speaking. The account does not say what He wrote, of course, but this would seem to be the most probable suggestion.