|Qasim ibn Muhammad
|Banu Hashim of Quraysh
|Died in Time of Ignorance
|Muhammad’s first son
Al-Qasim was Muhammad’s first son and the origin of his kunya Abu al-Qasim.
The first born child to the Apostle of Allah, may Allah bless him, was al-Qasim, who was born at Makkah before his being raised to prophethood, and after whom his patronymic was Abu al-Qasim. Then Zaynab was born to him, then Ruqayyah, then Fatimah, then Umm Kulthum, then after the advent of Islam `Abd Allah was born and he got the appellation of al-Tayyib (perfumed) and al-Tahir (pure). The mother of all of them was Khadijah Bint Khuwaylid Ibn Asad Ibn `Abd al-`Uzza Ibn Qusayyi; and her (Khadijah’s) mother was Fatimah Bint Zà’idah lbn al-Asamm Ibn Harim Ibn Rawahah Ibn Hujr Ibn `Abd Ibn Ma’is Ibn ‘Amir Ibn Luwayyi. The first of his children to die was al-Qasim, then `Abd Allah, at Makkah. Thereupon al-‘As Ibn Wa’il al-Sahmi said: His offspring have ceased and so he is abtar (without posterity).Ibn Sa’d
More evidence for al-Qasim is in Ibn Sa’d:
Verily the Prophet was at al-Bagi’, when a person called: O Abu al-Qasim! The Prophet turned to him. But (the man) said: I do not mean you. Thereupon the Prophetic said: Name after me, but do not take my patronymic (to you).
There’s another context for the same narration:
A son was born to an Ansari who named him Muhammad; consequently the Ansàr became angry and said: (We will not leave) till we ask the Prophet. Then they mentioned it to him. He said: The Ansar have done the right thing. Then he added: Name after me but do not apply my patronymic since I am Abu al-Qasim and distribute among you.
Al-Qasim means “the one who distributes,” so Abu al-Qasim can be both a kunya (patronymic) and also a description of a generous person, like Abu Lahab means “father of flame” and is a nickname for someone with pink cheeks. Muhammad here is taking his kunya as having the meaning of a nickname.
Another narration split the difference between the two:
Verily a person among the Ansar had his patronymic Abu al-Qàsim. Then the Ansar said: We will not let you have this patronymic unless we ask the Apostle of Allah, about it. Then they mentioned it to the Apostle of Allah, may Allah bless him, and he replied: Name after me but do not take my patronymic. Sa’id said: Qatadah disliked that a man should bear the patronymic of Abu al-Qasim although his name was not Muhammad.
There are a few more very confused or partial narrations, but these present the range of likely possibilities well enough.
All the sources make al-Qasim Muhammad’s oldest son. There is a goofy hadith in Bukhari that runs like this:
“When Qasim the son of the Messenger of Allah (ﷺ) died, Khadijah said: ‘O Messenger of Allah, the milk of Qasim’s mother is overflowing. Would that Allah had let him live until he had finished breastfeeding.’ The Messenger of Allah (ﷺ) said: ‘He will complete his breastfeeding in Paradise.’ She said: ‘If I know that, O Messenger of Allah, it makes it easier for me to bear.’ The Messenger of Allah (ﷺ) said: ‘If you wish, I will pray to Allah to let you hear his voice.’ She said: ‘O Messenger of Allah, rather I believe Allah and His Messenger.’”Sahih Bukhari 1:6:1512
It is (obviously) ruled weak because it’s anachronism is too ridiculous to support, since al-Qasim died long before the revelation of the Quran.
Another ahadith confirms the content of this, though without the anachronism:
Narrated Ali ibn Abu Talib: Khadijah asked Allah’s Apostle (peace be upon him) about her children who had died in the days of ignorance. Thereupon Allah’s Messenger (peace be upon him) said: They are in Hell Fire, and when he saw the sign of disgust on her face, he said: If you were to see their station you would hate them. She said: Allah’s Messenger, what about my child that was born of your loins? He said: It is in Paradise. Then Allah’s Messenger (peace be upon him) said: Verily the believers and their children will be in Paradise and the polytheists and their children in the Hell Fire. Allah’s Messenger (peace be upon him) then recited this verse: `And those who believe and whose offspring follow them in faith We unite with them their offspring and I shall deprive them of naught in their work.’Al-Tirmidhi 117
So even though Khadija became a believer in Islam, her children by other men were in Hell, while her son with Muhammad was in Paradise.