How? Crying and Weeping.
There are Ahadith in which the Prophet pbuh indicated and knew of the eventual martydom of Imam Hussain and the cruel way in which he was to be killed by people of his "ummah".
Widely reported Hadith in the Shia gatherings:
When the Holy Prophet(phuh&hf) informed Hazrat Fatimah(s.a.) of the Martyrdom in store for his grandson, she burst into tears and asked, "O my father! when would my son be martyred?" "In such a critical moment," he replied," When neither I nor you, nor Ali would be alive. " This accentuated her grief and she inquired again," Who then, O my father, would commemorate Hussain's martyrdom?". The Holy Prophet(pbuh&hf) said, "The men and the women of a particular sect of my followers, who will befriend my Ahl-ul-Bayt, will mourn for Hussain and commemorate his martyrdom each year in every century."
Others Hadith:
The Messenger of Allah (S.A.W.) wept for his grandson, Hussain (A.S.) on various occasions.
(i) Tradition of Ummul Fazl.
The first narration quoted by us is recorded in Mustadrakul Sahihayn, History of Ibne Asakir and Maqtal of Khwarizmi, other books also mention this incident.
Ummul Fazl the daughter of Harith came to the Messenger of Allah (S.A.W.) and said: "O Messenger of Allah (S.A.W.), I had a dream in which I saw that a piece of your flesh flew off and fell into my lap. The Messenger of Allah (S.A.W.) told her, "You have seen something good, by the will of Allah, Fatima will give birth to a child and you will be present in the house."
Later Fatima (S.A.) gave birth to Hussain (A.S.) and Ummul Fazl was present, as the Prophet (S.A.W.) had predicted. She placed Hussain (A.S.) in the lap of the Prophet (S.A.W.), She said:
"Thus when I saw the Messenger of Allah (S.A.W.) that his eyes were filled with tears. I said, 'O Messenger of Allah (S.A.W.), may my parents be sacrificed for you, why are you weeping?'.
He (S.A.W.) replied, 'Jibraeel came to me and informed me that my people will soon murder this son of mine.'
I asked, 'This son?'
'Yes', he (S.A.W.) replied, 'And he gave me the red dust of his grave.'
Al-Hakim says, "This is an authentic hadith according to the standards of Bukhari and Muslim, but they have not included it in their collections."
(ii) Tradition of Zainab Binte Jahash
A similar type of narration has been presented in the books: Tarikh Ibne Asakir, Majmauz Zawaed, Tarikh Ibne Kathir etc:
Zainab says: One day while Hussain (A.S.) was in my house and near me at the staircase, and then I became thoughtless. The Messenger of Allah (S.A.W.) entered.... He (S.A.W.) said, "Let him be (as he is). The Prophet (S.A.W.) stretched out his hands while he was performing the prayers and took Hussain (A.S.) to him. I said, "O Messenger of Allah (S.A.W.), I have never seen you do this before?"
He (S.A.W.) said, "Jibraeel came to me and informed me that this (Hussain) will be killed by my Ummat." I requested him, "Then show me the dust of the land, where he will be killed." And he gave me some red earth.
(iii) Tradition of Ayesha (R.A.)
Abi Salma has been recorded in Tarikh Ibne Asakir, Maqtal Khwarizmi and Majmauz Zawaid to say:
Ayesha (R.A.) said: The Messenger of Allah (S.A.W.) had seated Hussain (A.S.) upon his thigh when Jibraeel came and asked, "Is this your son?"
"Yes", he replied.
Jibraeel said, "But your Ummat will soon kill him after your demise."
The eyes of the Prophet filled with tears.
Jibraeel said, "Would you like to see the land where he shall be killed?"
"Yes", he replied.
Then Jibraeel showed him the fine dust of his grave.
In another narration there is a variation where Jibraeel is reported to have indicated towards Iraq and took some red dust from it and showed it to him and said, "This is the dust from his fatal battleground."
(iv) Tradition of Umm-e-Salma (R.A.)
Mustadrakul Sahihayn, Tabaqaat Ibne Saad, Tarikh Ibne Asakir and other books have mentioned the following tradition from Umm-e-Salma (R.A.):
The Messenger of Allah (S.A.W.) was sleeping one night when he awoke with a start. He was in a state of terror. Then again he went to sleep and once more woke up with a start. This time he was more worried. Again he went to sleep and woke up. In his hands was some red dust. He was turning it around in his hands.
She said, "What is this dust, O Messenger of Allah?" He said, "Jibraeel informed me that this Hussain will be killed in the land of Iraq. I asked Jibraeel to show me the dust of the land where he will be killed. And this is that dust."
Please cross reference them.