The sages say: (They were given) ten on one tablet and ten on the other. As it is written (Devarim 5:19) "These things (the ten commandments) the L–rd spoke … And He wrote them on two tablets of stone." And (Song of Songs 4:5) "Your two breasts are like two fawns, twins of a gazelle." And (Ibid. 5:14) ("The tablets of) His hands are wheels of gold, set with emeralds."...
While Rabbi Chanina Ben Gamliel on Five Commandments Appeared on Each
Mekhilta Tractate Bachodesh 8:22