Prophet Muhammad (P.B.U.H&H.P) wept whenever he was foretold the tragedy that would befall on Hussain (A.S) and his companions.
Musnad Abu Ya'la Mosuli, Volume 1 page 298 Hadith 363:
Abdullah ibn Naji narrated from his father who said: ‘I went with Ali, they faced Nainawa as they were going to the battle of Siffin then Ali called out and said: ‘O Aba Abdullah, have patience, O Aba Abdullah have patience on the bank of the Euphrates’. I asked: ‘What do you mean by Aba Abdullah’? Ali replied: ‘One day I went into the room of the Prophet (P.B.U.H&H.P) whilst his eyes were gushing with tears, I therefore asked of him: ‘O Prophet, has someone angered you? What makes your eyes gush with tears?’ He (P.B.U.H&H.P) replied: ‘Gabriel has just left me; he (Gabriel) told me that Hussain will be killed on the banks of the Euphrates River. Gabriel then said to him (P.B.U.H&H.P): ‘Shall I let you smell its soil (wherein Hussain will be killed)? I said: ‘Yes’. So Gabriel extended his hand and presented a handful of the soil and gave it to me, I was then unable to prevent my eyes from gushing into tears’’’.
We also read in Musnad Abu Ya'la Mosuli, Vol 6, p 129, Hadith 3402:
Anas bin Malik said: ‘The angel of rain asked permission from his Lord to visit the Holy Prophet (P.B.U.H&H.P) who granted permission. On that day the Prophet (P.B.U.H&H.P) was with Umm Salama. The Prophet (P.B.U.H&H.P) told her: ‘Guard the door and do not let anyone in’. While she was at the door, Hussain bin Ali burst into the room, so the Prophet (P.B.U.H&H.P) began to hug and kiss him. The angel said to Prophet (P.B.U.H&H.P): ‘Do you love him?”. He (P.B.U.H&H.P) replied: ‘Yes’. The angel said: ‘Your nation will kill him. If you wish, I can show you the place wherein they will kill him’. The Prophet (P.B.U.H&H.P) said: ‘Yes’. So the angel took a handful of soil from the spot of his (Hussain’s) murder and showed it and it was Sahla or red soil’. So Umm Salama took the soil and put it in her clothing’.
Al-Albaani records a ‘Sahih’ Hadith:
Gabriel came to me and informed me that my nation will kill my son Hussain. I asked: ‘This Hussain?’ He (P.B.U.H&H.P) replied: ‘Yes’ he then brought me some of its soil that was red. Narrated by Lubaba bint al-Harith that she went to the Holy Prophet (P.B.U.H&H.P) and said: ‘O Prophet, I have seen an unclear dream tonight’. He (P.B.U.H&H.P) asked: ‘What is it?’ She replied: ‘I saw that as if a part of your body was cut off from you and was placed upon my chest’. He (P.B.U.H&H.P) said: ‘You have seen something good. Inshallah Fatimah will bear a baby boy and he will be upon your chest.’ So Fatima gave birth to Hussain and he was on my chest as the Prophet (P.B.U.H&H.P) had notified me. On one day I went to the Holy Prophet (P.B.U.H&H.P) and put Hussain on his chest then he turned his face to the side and I witnessed his (P.B.U.H&H.P) eyes flowing with tears. I asked: “Prophet of Allah, my parents be sacrificed for you, what is wrong?” he (P.B.U.H&H.P) then mentioned it (the above hadith).
Silsilah Al-Ahadith Al-Sahiyah, Volume 2 page 462 Hadith 821.
We can see from these traditions that Prophet (P.B.U.H&H.P) was foretold about the martyrdom of Imam Hussain (A.S) on three separate occasions, by three different angels. Upon being notified of the tragic demise of his grandson, Prophet (P.B.U.H&H.P) broke down into tears, distraught at what was to become of him. On none of these occasions did Prophet (P.B.U.H&H.P) appear impassive and motionless at the news, his emotions overtook and his eyes were filled with tears when he was notified of what harm would befall his grandson (A.S). If Prophet (P.B.U.H&H.P) cried so profusely at the news of what was to happen to his grandson in the future, can one imagine his state would be on the Day of Karbala, when Hussain (A.S) was showered with arrows, his head decapitated and horses trampled over his body? This proves that crying when hearing of the suffering of Hussain (A.S) is a tradition (Sunnah) of Prophet (P.B.U.H&H.P).
The tradition can also be read in:
Al-Sawa'iq al-Muhriqah, page 641