Abdullah ibn Masud reported: The Messenger of Allah, peace and blessings be upon him, said:

Source: Ṣaḥīḥ al-Bukhārī 7454, Grade: Muttafaqun Alayhi

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 لَا إِلَهَ غَيْرُهُ إِنَّ أَحَدَكُمْ لَيَعْمَلُ بِعَمَلِ أَهْلِ الْجَنَّةِ حَتَّى مَا يَكُونُ بَيْنَهُ وَبَيْنَهَا إِلَّا ذِرَاعٌ فَيَسْبِقُ عَلَيْهِ الْكِتَابُ فَيَعْمَلُ بِعَمَلِ أَهْلِ النَّارِ فَيَدْخُلُهَا وَإِنَّ أَحَدَكُمْ لَيَعْمَلُ بِعَمَلِ أَهْلِ النَّارِ حَتَّى مَا يَكُونُ بَيْنَهُ وَبَيْنَهَا إِلَّا ذِرَاعٌ فَيَسْبِقُ عَلَيْهِ الْكِتَابُ فَيَعْمَلُ بِعَمَلِ أَهْلِ الْجَنَّةِ فَيَدْخُلُهَا

Verily, the creation of each one of you is brought together in his mother’s womb for forty days as a drop, then he is a clot for a similar period, then a morsel for a similar period, then there is sent to him the angel who blows the spirit into him and he is commanded regarding four matters: to write down his provision, his life span, his deeds, and whether he is blessed or damned. By Allah, other than whom there is no God, one of you acts like the people of Paradise until he is but an arm’s length from it, and what is written overtakes him so he acts like the people of Hellfire and he enters it. Verily, one of you acts like the people of Hellfire until he is but an arm’s length from it, and what is written overtakes him so he acts like the people of Paradise and he enters it.