(a part of ziyarat aashoora ):            

Translation of (assalamu alayk ya tharaallah wabni tharih walwitr almuwtur ):

" Peace be upon you O’ the one who was killed and whose blood has not yet been avenged – and whose avenging is in the hands of Allah and peace be upon you, the son of one who was killed and whose blood has not yet been avenged (Imam Ali ibne Abi Talib) and peace be upon you O’ the one who was alone, an individual (killed).”

In order to better understand this line, it is necessary to say that if a person  be killed it's avenger (qisas) be taken . But avenger of Imam Husain has not been taken yet.

But please note that with this said, we see in another Ziyarat of Imam Husain that we pray,

“And surely you are the (metaphorical) blood of Allah on the earth and you are the blood which has not be avenged by a single person on the Earth and which can not be avenged except by Allah, the One.”

 Therefore, the ‘avenger’ mentioned in this Ziyarat is not the avenger of an act done by one person upon another person since in this case it would have been settled between Imam Zaynul Abideen (AS) and Shimr, Yazid and the others. This is not a killing which could be avenged in a few hours and with the killing of a few people. Rather, this is a case of avenging the death of a person who was the representative of Allah over all of humanity for all time and is something which can only be carried out by the One who had sent such a representative. In closing, we recall the words of our 6th Imam in Dua-e-Nudbah where he cries out to the one who shall avenge the blood on behalf of Allah,

“Where is the one who shall avenge the blood of the murdered Prophets and the sons of the Prophets who were murdered? Where is he one who shall avenge the blood of those killed in Kerbala?”

Yes, Imam Mahdi (As) will come to take avenge of Imam Husain (as) and also Hazrat Fatimah (SA).

So pray much to Allah to hasten the Relief (zuhur of Imam zaman (as))..