פירוש על ברכות 61:2

HE BOUGHT A CUP OF WHITE GLASS. The Gemara relates that at the wedding of Rav Ashee’s son, Rav Ashee saw that the students were getting a bit too happy. He brought a very expensive cup and broke it in front of them in order to stem the overflow of happiness. From here, it became customary to break a cup at a wedding. This custom remains with us till today