Translation:Mishnah/Seder Moed/Tractate Sukkah/Chapter 2/1
One who sleeps underneath the bed inside the sukkah has not fulfilled their obligation.
Rabbi Yehudah said, "It was our custom that we would sleep underneath the bed in front of the elders and they did not say anything to us".
Rabbi Shimon said, "There was a story with Tovi the slave of Rabban Gamliel that he would sleep underneath the bed and Rabban Gamliel said to the elders, 'Have you seen Tovi my slave that he is a scholar and he knows that slaves are free from the (mitzvah of) sukkah, therefore he sleeps underneath the bed!'"
And according to our way we learn, that one who sleeps underneath the bed has not fulfilled their obligation.