Extract from Nur al-Uyun (Biography of the Prophet) by Imam ibn Sayyid an-Nas | ridawipress.org
Qasim, and it is on his account that the Messenger of Allah has the appellation of Abu’l Qasim.
Tayyib – Tahir; it is also said that Tayyib is different from Tahir (that they are two sons and not one).
and Fatimah. May Allah Most High be pleased with them all.
His sons passed away in infancy and before the rise of Islam; but his daughters lived and all of them accepted Islam. All his children [mentioned above] were borne by Sayyida Khadijah. In Madinah, a son Ibrahim was born from Mariyah; but he passed away as an infant. It is said that he was either seventy days, or seven months, or eighteen months old at the time of his demise.1
All his children except Sayyida Fatimah passed away in his lifetime.2 Fatimah demised six months after the passing of the Messenger of Allah.
1 The latter narration of eighteen months (one and a half year) old is widely accepted.
2 His life in this world, because Prophets are alive in their graves.