Sahih Muslim 2646
Anas b. Malik reported directly from Allah's Messenger (ﷺ) that he said:
Allah, the Exlated and Glorious, has appointed an angel as the caretaker of the womb, and he would say: My Lord, it is now a drop of semen; my Lord, It is now a clot of blood; my Lord, it has now become a lump of flesh, and when Allah decides to give it a final shape, the angel says: My Lord, would it be male or female or would he be an evil or a good person? What about his livelihood and his age? And it is all written as he is in the womb of his mother.
حَدَّثَنِي أَبُو كَامِلٍ، فُضَيْلُ بْنُ حُسَيْنٍ الْجَحْدَرِيُّ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، حَدَّثَنَا عُبَيْدُ،
 اللَّهِ بْنُ أَبِي بَكْرٍ عَنْ أَنَسِ بْنِ مَالِكٍ، وَرَفَعَ الْحَدِيثَ، أَنَّهُ قَالَ ‏
"‏ إِنَّ اللَّهَ عَزَّ وَجَلَّ قَدْ وَكَّلَ
 بِالرَّحِمِ مَلَكًا فَيَقُولُ أَىْ رَبِّ نُطْفَةٌ أَىْ رَبِّ عَلَقَةٌ أَىْ رَبِّ مُضْغَةٌ ‏.‏ فَإِذَا أَرَادَ اللَّهُ أَنْ يَقْضِيَ
 خَلْقًا - قَالَ - قَالَ الْمَلَكُ أَىْ رَبِّ ذَكَرٌ أَوْ أُنْثَى شَقِيٌّ أَوْ سَعِيدٌ فَمَا الرِّزْقُ فَمَا الأَجَلُ
 فَيُكْتَبُ كَذَلِكَ فِي بَطْنِ أُمِّهِ ‏"‏ ‏.‏