Way back in 1998, on MBD's "English Collection," he published a song titled "Daddy Dear" depicting a dialogue between a son and his father regarding a cup Hashem supposedly has in Shamayim into which He cries when the Bnei Yisrael are hurt. When the cup is full, we will be redeemed. The song ends with a plea from the father-son duo that the cup should finally be filled and our tzaros completed.
Is there a Midrash or Gemara behind this song? Is there any basis to it other than a mashal the songwriter came up with to explain why we haven't been redeemed yet - that our metaphorical cup of tzaros hasn't runneth over?