(1) بَابُ خَلْقِ آدَمَ صَلَوَاتُ اللَّهِ عَلَيْهِ وَذُرِّيَّتِهِ
Narrated Anas bin Malik:
The Prophet (ﷺ) said, "Allah has appointed an angel in the womb, and the angel says, 'O Lord! A drop of discharge (i.e. of semen), O Lord! a clot, O Lord! a piece of flesh.' And then, if Allah wishes to complete the child's creation, the angel will say. 'O Lord! A male or a female? O Lord! wretched or blessed (in religion)? What will his livelihood be? What will his age be?' The angel writes all this while the child is in the womb of its mother."
Reference: Sahih al-Bukhari 3333
In-book reference: Book 60, Hadith 8
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 55, Hadith 550