هُوَ الَّذِي خَلَقَكُم مِّن طِينٍ
He it is Who has created you from clay,
refers to the father of mankind, Adam, from whom mankind originated, multiplied in numbers and spread about, east and west.
Allah said,
ثُمَّ قَضَى أَجَلً وَأَجَلٌ مُّسمًّى عِندَهُ
Then has decreed a stated term. And there is with Him another determined term...
His saying;
ثُمَّ قَضَى أَجَلً
(Then has decreed a stated term),
refers to death,
while,
وَأَجَلٌ مُّسمًّى عِندَهُ
(And there is with Him another determined term...),
refers to the Hereafter,
according to Sa`id bin Jubayr who reported this from Ibn Abbas.
Similar statements were narrated from Mujahid, Ikrimah, Sa`id bin Jubayr, Al-Hasan, Qatadah, Ad-Dahhak, Zayd bin Aslam, Atiyah, As-Suddi, Muqatil bin Hayyan and others.
Ibn Abbas and Mujahid said that,
ثُمَّ قَضَى أَجَلً
(And then has decreed a stated term),
is the term of this earthly life,
while,
وَأَجَلٌ مُّسمًّى عِندَهُ
(And there is with Him another determined term),
refers to man's extent of life until he dies as mentioned in Allah's statement;
وَهُوَ الَّذِي يَتَوَفَّاكُم بِاللَّيْلِ وَيَعْلَمُ مَا جَرَحْتُم بِالنَّهَارِ
It is He, Who takes your souls by night (when you are asleep), and has knowledge of all that you have done by day, then He raises (wakes) you up again that a term appointed (life) be fulfilled. (6;60)
The meaning of Allah's statement,
عِندَهُ
(With Him), is that;
none but Him knows when it will occur.
Allah said in other Ayat,
إِنَّمَا عِلْمُهَا عِنْدَ رَبِّي لَا يُجَلِّيهَا لِوَقْتِهَأ إِلاَّ هُوَ
The knowledge thereof is with my Lord. None can reveal its time but He. (7;187)
and,
يَسْأَلُونَكَ عَنِ السَّاعَةِ أَيَّانَ مُرْسَـهَا
فِيمَ أَنتَ مِن ذِكْرَاهَا
إِلَى رَبِّكَ مُنتَهَـهَأ
They ask you about the Hour -- when will be its appointed time! You have no knowledge to say anything about it. To your Lord belongs (the knowledge of) the term thereof. (79;42-44)
Allah said,
ثُمَّ أَنتُمْ تَمْتَرُونَ
Yet you doubt.
According to As-Suddi,
the coming of the (last) Hour.
Allah said next,
وَهُوَ اللّهُ فِي السَّمَاوَاتِ وَفِي الَارْضِ يَعْلَمُ سِرَّكُمْ وَجَهرَكُمْ وَيَعْلَمُ مَا تَكْسِبُونَ