Muḥammad ibn ʿAbd Allāh ibn Jaʿfar (Arabic: محمد بن عبدالله بن جعفر) was Zaynab's son.
His paternal grandfather was Ja'far al-Tayyar, whom Muhammad (the prophet) had appointed as the head of the emigrants to Abyssinia.
[1] When Husayn ibn Ali moved from Mecca to Medina, Abd Allah ibn Ja'far wrote a letter to the Husayn and tried to change his mind.
He sent the letter through his sons Muhammad and Awn, but when Abd Allah ibn Ja'far realized that the Imam is determined to go, he advised Muhammad and Awn to accompany Husayn ibn Ali.
[2] Muhammad fought bravely and killed 10 warriors of enemy's army, but at the end was killed by Amir ibn Nahshal al-Tamimi.