Musnad Ahmad 286:2

Sufyan narrated to us, from ‘Amr, from Abu al-Tufayl, from Hudhayfah ibn Asid al-Ghifari, who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him)—or he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The angel enters upon the drop of semen after it has settled in the womb for forty nights—and Sufyan said once: or forty-five nights—and he says: 'O Lord, is he wretched or happy? Is he male or female?' So Allah, Blessed and Exalted is He, speaks, and they [the angel and his scribe] write. Then they say: 'What? Is he male or female?' So Allah, Mighty and Majestic is He, speaks, and they write. Then they write his deeds, his lifespan, his affliction, and his provision. Then the scroll is rolled up, and nothing is added to what is in it, nor is anything taken away."