The Simcha of a Siyum
The Mishna at the end of Taanis (26b) quotes Rabban Shimon Ben Gamliel who declares that the most joyous holidays on the Jewish calendar are Yom Kippur and Tu B’Av.
Birkas HaMazon
Whether the phrase added to the zimun at weddings and sheva brachos should also be said in bentching at a siyum.
The Mishna at the end of Taanis (26b) quotes Rabban Shimon Ben Gamliel who declares that the most joyous holidays on the Jewish calendar are Yom Kippur and Tu B’Av.