The Prophet (pbuh) had numerous times said, "Hassan and Hussain are my children. Whoever loves them has indeed loved me." Because of these words, Imam Ali (as) used to say to his other children, "You are my children and Hasan and Hussain are the children of the Prophet."
Imam Hassan Mujtaba (as) was the second Imam. He and his brother Imam Hussain were the two sons of Amir al-Mu'minin Ali (as) and Hadhrat Fatimah (as), the daughter of the Prophet (pbuh). The Prophet (pbuh) had numerous times said, "Hassan and Hussain are my children. Whoever loves has indeed loved me." (Ibn Asakir, History of Damascus, vol. 106, p. 59) Because of these words, Imam Ali (as) used to say to his other children, "You are my children and Hasan and Hussain are the children of the Prophet."
Imam Hassan (as) was born in the year 3 A.H. in Medina and shared in the life of the Prophet (pbuh) for somewhat over seven years, growing up during that time under his loving care. After the death of the Prophet (pbuh) which was no more than three, or according to some, six months earlier than the death of Lady Fatima (a.s.), Imam Hassan (a.s.) was placed directly under the care of his noble father.
On the 21st night of the month of Ramadhan of 40th Hijra his father Imam Ali ibn-e-Abi Talib (as) passed away making all the people sorrowful and grieved.
Imam Hassan (as) who was 27 years of age came along with the people to the mosque and climbed the tribune and said, "Last night, a man, who was unique in knowledge, piety, conduct, and character amongst people of the previous ages as well amongst those to come in future, left you. He participated the battles along with the Prophet Muhammad (pbuh) and strived hard to guard Islam. A person who was the thorn in the eyes of the enemies and the fruit of the heart of the riends. He did not accumulate anything from the wealth of the world for himself, except for seven hundred Dirhams by which he wanted to provide a servant for his family." (Nourullah Shushtari, Ihqaq al-Haqq, Edited by Shahab al-Din Mar'ashi, vol. 11, pp. 93-182)