The term "Sasson [Joy]" as a reference to the Mitzvah of Circumcision: Megillah 16b
Hashem made Avraham 13 Covenants on Circumcision: Shabbat 132a, 133a; Nedarim 31b
Circumcision is considered an "Ot", a Sign, Between Hashem and the Jews: Shabbat 132a
If not for the blood of Circumcision, Gd would not have created the World: Nedarim 31b
If not for the blood of Circumcision, Gd would not have maintained Creation: Shabbat 137b [2x]; Nedarim 32a
Circumcision was accepted with joy, and so it was maintained throughout the generations: Shabbat 130a
Because the Jews Martyred themselves for Circumcision, it has stayed strong with their descendants: Shabbat 130a
The piece of skin which is to be cut off is considered disgusting: Nedarim 31b
The wicked are identified as people of the skin which is to be cut off in circumcision: Nedarim 31b
Moses was born circumcised: Sotah 12a
Does Yom Kippur atone for a Jew who refuses to have a circumcision: Yoma 85b; Keritot 7a