These words are from the concealed codes regarding which Allah informed His Servant the Prophet Zakariyah (a.s.) and regarding which it was revealed to the Holy Prophet Mohammad (s.a.w.s.).

Prophet Zakariyah (a.s.) asked his Lord to teach him the names of the Five Pure Ones, to which Jibra'eel descended and taught him the five names. Whenever Prophet Zakariyah (a.s.) recited the four names, Mohammad (s.a.w.s.), Ali (a.s.), Fatemah (a.s.) and Hasan (a.s.), his heart would be enlightened and his sorrow would part away, but when he took the name of Husain (a.s.) he would become sorrowful and turn restless. One day he asked Allah Almighty, "My Lord! When I utter the names of these four Pure Personalities, my sorrow parts away, but when I take the name of Husain, I turn sorrowful and weep & wail." Then Allah, the Mighty the Sublime revealed to him regarding Kaf, Ha, Ya, Ain, Swad.

Kaf stands for Karbala,
Ha for Halakah (perdition) of the Prophet's Household,
Ya for Yazid, the oppresser and murderer of Husain (a.s.),
Ain for Atash (thirst), and
Swad for (Sabr) Patience and forbearance of Husain.

When Prophet Zakariyah heard this he was so much grieved that for three consecutive days he refused to come out of his place of worship and did not permit people to meet him, and remained grief-stricken and wept profusely. And he recited the following elegy: “O Lord! Will you let the best of Creatures see the plight of his son? O Lord! Will you allow this disaster to fall upon his House-hold? O Lord! Will you let Ali and Fatemah wear the dress of grief and will they witness this calamity"?

He (Prophet Zakariyah) would always say, "O Lord! Bestow upon me with a son who would be the light of my eyes in my old-age, and when you present me with a son make my love intense for him and then let me taste the grief of his loss as Your Friend Mohammad (s.a.w.s.) who will mourn the death of his son. Thus Allah blessed Prophet Zakariyah (a.s.) with a son Prophet Yahya (a.s.) whose death was mourned by Prophet Zakariyah. Prophet Yahya (a.s.)'s period of (his mother's) pregnancy was six months similar to that of Imam Husain (a.s.)."

(This tradition has been quoted from Imam Mahdi a.s. – Nafsul Mahmoom)