Sotah, chapter 9, mishnah 11. Continuing the list of things that ceased, the mishnah states: "Mishebatlah Sanhedrin - batel hashir mibeis hamishta'os, shene'emar: 'bashir lo yishtu yayin'" - from the time the Sanhedrin ceased, song ceased from the drinking houses, as it says: "They shall not drink wine with song."
Explanation of the words of the mishnah:
"Mishebatlah Sanhedrin" - from the time that the Sanhedrin no longer sat in Jerusalem, after they were already no longer there in the days of the Second Temple. From that time "batel hashir mibeis hamishta'os": singing stopped in the places where people drink wine together, such as at a wedding and the like. The reason for this is derived from the verse in Yeshayah - "bashir lo yishtu yayin" - they do not drink wine accompanied by song, and it is the joining of song to wine that ceased.
The Gemara's question and the source of the law:
The Gemara notes that from the verse in Yeshayah there is no indication that the matter is connected to the ceasing of the Sanhedrin, and therefore it brings a different verse, in Eichah: "zekeinim misha'ar shavasu, bachurim mineginasam".
"Zekeinim misha'ar shavasu" - the elders, meaning the Sanhedrin, no longer sit in the gate and are no longer present in the Temple.
"Bachurim mineginasam" - and because of this the young men ceased from their music and their song.
It emerges that from the time we no longer had the elders in the gate - that is, the Sanhedrin - they stopped singing.
In practice - which songs ceased:
The halachic authorities explain that we are speaking here of songs that do not deal with the kindness of the Holy One, blessed is He; but songs connected to the kindness of the Holy One, blessed is He - it is the practice of all Israel to sing them at weddings and celebrations, even when there is drinking there.
In summary: In this mishnah we learned that from the time the Sanhedrin ceased, song ceased from the drinking houses, its source being the verse "They shall not drink wine with song"; that the Gemara anchored this law in the verse "The elders have ceased from the gate, the young men from their music" - which links the end of the elders' sitting in the gate to the end of the young men's music; and that in practice this was said regarding songs that are not about the kindness of the Holy One, blessed is He, while songs of the kindness of Heaven are the practice of all Israel at weddings and celebrations, even where there is drinking.