The Prophet Muhammad SAW once kept weeping the whole night through, repeating again and again the following verse:
"If Thou punish them, they art Thy slaves; and if Thou forgive them, Thou only art The Mighty, The Wise." (Surah 5: Ayat 118)
This quality of weeping in Solat is practiced by those close to Allah SWT.
It is narrated about the grand Mujtahid of fiqh - Imam Abu Hanifah RA that he also once wept the whole night, reciting the following verse of the Qur'an in Tahajjud:
"But avaunt ye, 0, ye guilty, this day." (Surah 36: Ayat 58)
This verse means that on the Day of Judgement, the guilty will be asked to separate themselves from the good, and will not be allowed to mix with them, just as they were doing in the worldly life.
It is only common sense that any slave of Allah who have their hearts inculcated with the fear of Allah would weep in anxiety about this, as who knows as to which class they belong to on the Day of Judgement?