Hudhaifa b. Usaid (RA) reported directly from Allah’s Messenger (SAW) that he said:
When the drop of (semen) remains in the womb for forty or forty five nights, the angel comes and says: My Lord, will he be good or evil? And both these things would be written. Then the angel says: My Lord, would he be male or female? And both these things are written. And his deeds and actions, his death, his livelihood; these are also recorded. Then his document of destiny is rolled and there is no addition to nor subtraction from it.
Sahih Muslim 2644, Book 46, Hadith 3