Arachin 12 - Bad Things Happen on a Bad Day
Is the Levites's singing required for libations in the Temple? Since libations include wine, and the Levites started singing when wine was poured on the Altar, maybe it is required; on the other hand, since there is no meat with libations, maybe it is not required?
Let us try to find an answer in the story of the Temples' Destruction, as related by Rabbi Yose: "Good things are brought about on an auspicious day, and bad things - on a bad day. It was the first day of the week and the first year after Shmita, and the Levites were singing 'God turned their violence against them', and just as they concluded with 'God our Lord will cut them off' the enemies came and vanquished them; and so it was at the destruction of the Second Temple."
Now, why were they singing? The daily sacrifice stopped a while back, so it must have been the libations, which proves that libations require singing. - Not necessarily, maybe they chanced upon a calf. Furthermore, as Rava said, it would be the wrong song for Sunday anyway, and it just happened that they started singing a dirge, for Resh Lakish said that Temple song can be performed without a sacrifice. But if so, let them sing for libations! - No, if we allow singing for a sacrifice that does not require singing, they may eventually skip singing when it is requried.
Art: Jan Jozef, the Younger Horemans - Lesson of Singing