In 17th day of Rabio_al_aval month in 82 hejri year one child from Imam Mohammad Baqir's(A.S) loins in ZeynolAbedin's(A.S) home in Medina. He had been famous to Jafar sadiq(A.S).

Some one written that his birthday's year is coincident with flood year in Mecca that is so famous.
This flood's power was so strong that it carried a lot of hajjis with it self. Its wave rolls a camel and damaged God's house.
Imam Baqir(A.S) wasn't in Mecca in Imam sadiq's(A .S) birthday.

His name:
They called him Jafar and they inspired from Prophet Mohammad's speech in this calling. There are a lot of speeches and narrative from Prophet Mohammad.
Like as:
God brings a child from Imam Baqir(A.S) rigid body,that he is Islamic truthful tongue, and he commanded that. Who want to look God should have his act's book in his right hand and should like Imam sadiq(A.S).