When Fatima az-Zahra (sa) was twelve, she became pregnant with Imam Hasan (as). Thus, the light of Imamate was carried on from ‘Ali (as) unto Fatima az-Zahra (sa). The day the child was to be born was approaching; the Prophet (S) had to go out of town, but before leaving, he (as) made several instructions about the would be born child, including the order not to wrap the new baby in a yellow cloth.
On Ramadhan 15, 3 A.H., Fatima az-Zahra (sa) gave birth to her first son. On that great day, Asma Bint Umais was present with Fatima az-Zahra (sa). The women who attended the event, unintentionally wrapped Al-Hasan (as) in a yellow cloth; they were not aware of the Prophet's (as) request.
When the Prophet returned, he said:
"Bring me my son; what have you named him?"
After Al-Hasan (as) was born Fatima az-Zahra (sa) asked ‘Ali (as) to name the baby, but ‘Ali (as) said: "I would not name him before Allah's Prophet".
When the Prophet saw that Al-Hasan was wrapped in a yellow cloth, he said: "Didn't I tell you not to wrap him in a yellow cloth?"
He then threw the yellow cloth away and wrapped the baby in a white one. When the Prophet inquired about the name of the child, ‘Ali (as) answered:
"I would not name him before you."
The Prophet (S) replied: "I too, would not name him before my Lord, Glory be to Him."
At that moment Allah revealed to Gabriel:
'A son was born to Muhammad, therefore descend and give him My blessings and congratulate him and say: "Surely ‘Ali is to you as Haroun was to Musa, so give him (the newborn baby) the name of Haroun's son:"'
When Gabriel had revealed the message to the Prophet, he asked: "What was Haroun's son's name?"
Gabriel said: "Shubbar."
The Prophet (S) then said: "My tongue is Arabic."
Gabrial said: "Name him Al-Hasan."
Hence, the Prophet (S) gave him the name Al-Hasan (as), and made Adhan in his right ear, and Eqamah in his left ear. On the seventh (7th) day, he (Prophet (S)) sacrificed two rams from which he gave the midwife a thigh, and a dinar; he then shaved the baby's head and gave as charity the weight of his hair in silver. Finally, the Prophet (S) wiped the baby's head with "Khalou" which is a special perfume made of saffron and other substances.
At that time in history, it was customary to cover newborn babies' heads with blood; with this in mind, the Prophet (S) told Asma:
"Asma, using blood is an act performed by the ignorant."
He would embrace Al-Hasan (as) and put his tongue in the baby's mouth, which would suckle it.