Sahih Muslim | Book 33 | Hadith Number 6397
Narrated by Anas b. Malik
Anas b. Malik reported directly from Allah's Messenger (may peace be upon him) that he said: Allah, the Exalted 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.