Lest there be any misunderstanding...
Lest there be any misunderstanding, it should be clarified here that the mourning for Imam Husayn is not a bid 'ah (innovation) at all. It was started by the Holy Prophet of Islam himself, more than 50 years before the event; and he was seen in a vision by the Mother of the believers, Umm Salmah, on the day of Husayn's martyrdom, mourning for Husayn. And Allah has ordered thousands of angels to weep on the grave of Imam Husayn till the day of resurrection.
These traditions are narrated in the Sunni books, and show that this particular mourning is the sunnah of the Holy Prophet and of the angels: Some 50 years before the event of Karbala, the Prophet wept when he was told by the angel that Husayn would be killed by the army of Yazid in Karbala. Then Gabriel asked, "O Prophet of God, do you want me to give you some earth from his place of martyrdom ?" The Prophet said, "Yes".
Gabriel gave him a handful of earth of Karbala and the Prophet began weeping uncontrollably. This tradition is recorded in Mishkatul-Masabih, Musnad of Imam Ahmad bin Hanbal, as-Sawaiqul Muhriqah of Allamah Ibn Hajar Makki and Sirrul-'alamin of Imam Ghazali; and has been narrated by Imam Sha'abi, Imam Baihaqi, Imam Hakim and scores of other traditionalists.
The Prophet gave that earth to his wife, Ummul Mu'mineen, Umm Salmah, and told her, "When you see this earth turned into blood, know that Husayn has been martyred." On the 10th Muharram, 61 A.H., Umm Salmah was asleep in the afternoon when she saw the Prophet in her dream: He stood there in a tragic coadition, his hair was dusty and dishevelled, and in his hand was a bottle full of blood. Umm Salmah asked him what it was. The Prophet said, "This is the blood of Husayn and his companions.
I was collecting it since this morning." Umm Salmah woke up and hurried towards the bottle which contained the earth of Karbala; she saw red blood flowing from it. Then she cried and called her relatives and started mourning for Husayn. This tradition is narrated in Musnad of Imam Ahmad bin Hanbal, as-Sawaiqul Muhriqah, Mishkatul-Masabih, Sahih of Tirmidhi and other books. Shaikh 'Abdul Qadir Jilani writes ia his book Ghunyatut-Talebeen, Vol.