Is it really an obligatory mitzvah to hear a reading of the Ten Commandments on the first day of Shavuot (as distinct from the general commandment to hear Torah)? What is the source, if any, for this mitzvah?
Motive: Chabad is very big on this "mitzvah." The Chabad Houses tell people to do it, and Chabad says in one place online, "All must attend the reading of the Ten Commandments, men and women, young and old." Is this true?