The months of mourning the grandson of the Prophet who was killed in Kerbala also see the marking of the martyrdom of the other grandson of the Prophet (SAW).
Born in the middle of the month of Ramadhan just three years after the Hijrah, Imam Hasan ibne Ali al-Mujtaba was the first-born of Ali al-Murtaza and Fatimah az-Zahra (peace be upon both of them). Establishing the Sunnah from this birth, the Prophet pronounced the Adhan and Iqamah in his right and left ears respectively and named him Hasan under Divine decree conveyed through the Angel Jibreel.
Without doubt, growing under the shadow of such noble personalities as Prophet Muhammad, Imam Ali ibne Abi Talib and Fatimah az-Zahra had a great impact on his upbringing and nurturing. In addition, this young child was also blessed to be one of the five “Ahlul Kisa” and the person referred to in the verse of Mubahilah and Suratul Insaan. All of these tributes granted him a great honour and distinction throughout the Muslim lands.
The historians are quick to note that as this young child grew, he more and more resembled his grand-father - the Messenger of Allah – both in physical looks and also in his morals and etiquette. This is something which the early Muslims kept in mind when they dealt with him, however as time went on, something which the Muslims threw behind their backs and neglected.
After the killing of his father in the Masjid of Kufah, Imam Hasan took over the Imamate of the community. However, due to the state of politics, after years of seeking to guide the community, the Imam was forced to sign a peace treaty with Muawiyah ibne Abu Sufyan, the enemy of Islam. Without doubt, this was not something easy for the Imam to do, however based on the greater interests of Islam, he had to do what he was ordered to by his Creator.
History tells us that from day one Muawiyah did not comply with any of the terms of the treaty agreed upon between him and Imam Hasan. To show his disdain with Islam, he boldly proclaimed, “Do you think I have taken power to teach you about Islam!? No, I have taken power for the sake of power and if any one of you tries to disagree with me, he shall pay a costly price by losing his head.”
Muawiyah’s hatred for Islam culminated when he convinced the wife of Imam Hasan, Juda bint Ashath to poison her husband – an event which culminated with Imam's death on the 7th of Safar.
In his last will and testament, the Imam asked his brother Imam Husain to take his body to the grave of their grand father the Prophet of Islam and bury him in that sacred spot. However, as the enemies of Islam would have it, his body was not only prevented from burial in that area, rather, arrows were shot at the casket carrying his body until Imam Husain was forced to retreat and bury his brother in Jannatul Baqi – according to some, in the precincts of his mother, Fatima az-Zahra. - Souce: http://www.world-federation.org/Secretariat/Articles/Commemorating+the+Wafat+of+Imam+Hassan+%28AS%29.htm