Exodus 19:11

19:11 and be ready for the third day, for on the third day the Lord will come down on Mount Sinai in the sight of all the people.

Exodus 19:15

19:15 He said to the people, “Be ready for the third day. Do not go near your wives.” ¹ 

[19:15]  ¹ tn Heb “do not go near a woman”; NIV “Abstain from sexual relations.”