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 Book 46, Hadith 3
← Previous Hadith " The creation of any one of you is like this that (semen) is collected in the womb of the mother for forty nights," and in the hadith transmitted on the authority of Shu'ba (the words are):" Forty nights and forty days." And in the hadith transmitted on the authority of Jarir and 'Isa (the words are):" Forty days."

Sahih Muslim Book 46, Hadith 2 Next Hadith → Evil one is he who is evil in the womb of his mother and the good one is he who takes a lesson from the (fate of) others. The narrator came to a person from amongst the Companions of Allah's Messenger (ﷺ) who was called Hudhaifa b. Usaid Ghifari and said: How can a person be an evil one without (committing an evil) deed? Thereupon the person said to him: You are surprised at this, whereas I have heard Allah's Messenger (ﷺ) as saying: When forty-two nights pass after the semen gets into the womb, Allah sends the angel and gives him shape. Then he creates his sense of hearing, sense of sight, his skin, his flesh, his bones, and then says: My Lord, would he be male or female? And your Lord decides as He desires and the angel then puts down that also and then says: My Lord, what about his age? And your Lord decides as He likes it and the angel puts it down. Then he says: My Lord, what about his livelihood? And then the Lord decides as He likes and the angel writes it down, and then the angel gets out with his scroll of destiny in his hand and nothing is added to it and nothing is subtracted from it.

Sahih Muslim Book 46, Hadith 4