I think it’s the Nesivos Shalom who brings this down in his Sefer:
“Al naharos Bavel… Shum Yushavnu Ve gam
- BUCHINU
“
He brings down a little known medrash.
When the Jews were being led to Bavel, Yirmiyahu (who was the Navi at the time) was given the choice to come to Bavel abd be given a good position, or remain in Yerushalayim. Yirmiyahu chose to remain in Yerushalayim to be with the remaining Jews there.
When the Jews who were going to Bavel heard his desicion, they cried!
“Yermiyahu! Don’t leave us!”
and Yirmiyahu responded:
“Had you cried just one tear, just one, you would not be going into Galus”
ONE TEAR?, he asks?
How could one tear have saved the Yidden? They needed to do Teshuva!
and with this he concludes with a powerful message:
Had the Jews shed one tear BEFORE this- they would have showed their pain, upset, sorrow- that would have been enough.
Just one pure tear is enough to bring the final Geula…