זוהר שמות — דף קצה ע”ב

The two stone Tablets broke because the letters flew away from them. At the four seasons of the year, a voice awakens in the four corners of the world, and this awakening of the impure side causes women their periodic impurity. The mourners of Zion and those who weep over the Temple’s destruction begin at the middle four hours with the psalm "By the rivers of Babylon." Heavenly angels weep with Israel in heaven, as it is said: "Here the angels cried out.”