Sahih Muslim 2643 a
Abdullah (b. Mas'ud) reported that Allah's Messenger (ﷺ) who is the most truthful (of the human beings) and his being truthful (is a fact) said:
Verily your creation is on this wise. The constituents of one of you are collected for forty days in his mother's womb in the form of blood, after which it becomes a clot of blood in another period of forty days. Then it becomes a lump of flesh and forty days later Allah sends His angel to it with instructions concerning four things, so the angel writes down his livelihood, his death, his deeds, his fortune and misfortune. By Him, besides Whom there is no god, that one amongst you acts like the people deserving Paradise until between him and Paradise there remains but the distance of a cubit, when suddenly the writing of destiny overcomes him and he begins to act like the denizens of Hell and thus enters Hell, and another one acts in the way of the denizens of Hell, until there remains between him and Hell a distance of a cubit that the writing of destiny overcomes him and then he begins to act like the people of Paradise and enters Paradise.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، وَوَكِيعٌ، ح وَحَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ،
 اللَّهِ بْنِ نُمَيْرٍ الْهَمْدَانِيُّ - وَاللَّفْظُ لَهُ - حَدَّثَنَا أَبِي وَأَبُو مُعَاوِيَةَ وَوَكِيعٌ قَالُوا حَدَّثَنَا الأَعْمَشُ،
 عَنْ زَيْدِ بْنِ وَهْبٍ، عَنْ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم وَهُوَ الصَّادِقُ
 الْمَصْدُوقُ ‏
"‏ إِنَّ أَحَدَكُمْ يُجْمَعُ خَلْقُهُ فِي بَطْنِ أُمِّهِ أَرْبَعِينَ يَوْمًا ثُمَّ يَكُونُ فِي ذَلِكَ عَلَقَةً مِثْلَ
 ذَلِكَ ثُمَّ يَكُونُ فِي ذَلِكَ مُضْغَةً مِثْلَ ذَلِكَ ثُمَّ يُرْسَلُ الْمَلَكُ فَيَنْفُخُ فِيهِ الرُّوحَ وَيُؤْمَرُ بِأَرْبَعِ كَلِمَاتٍ
 بِكَتْبِ رِزْقِهِ وَأَجَلِهِ وَعَمَلِهِ وَشَقِيٌّ أَوْ سَعِيدٌ فَوَالَّذِي لاَ إِلَهَ غَيْرُهُ إِنَّ أَحَدَكُمْ لَيَعْمَلُ بِعَمَلِ
 أَهْلِ الْجَنَّةِ حَتَّى مَا يَكُونَ بَيْنَهُ وَبَيْنَهَا إِلاَّ ذِرَاعٌ فَيَسْبِقُ عَلَيْهِ الْكِتَابُ فَيَعْمَلُ بِعَمَلِ أَهْلِ
 النَّارِ فَيَدْخُلُهَا وَإِنَّ أَحَدَكُمْ لَيَعْمَلُ بِعَمَلِ أَهْلِ النَّارِ حَتَّى مَا يَكُونَ بَيْنَهُ وَبَيْنَهَا إِلاَّ ذِرَاعٌ
 فَيَسْبِقُ عَلَيْهِ الْكِتَابُ فَيَعْمَلُ بِعَمَلِ أَهْلِ الْجَنَّةِ فَيَدْخُلُهَا ‏"‏ ‏.‏