Musnad Ahmad 26:6

Hashim narrated to us, he said: Ali ibn Zayd informed us, he said: I heard Abu Ubaydah ibn Abdullah narrating, he said: Abdullah said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The drop (nutfah) remains in the womb for forty days in its state, not changing. When the forty days have passed, it becomes a clinging clot (alaqah), then a chewed-like lump (mudghah) likewise, then bones likewise. When Allah wills to complete His creation, He sends an angel to it. The angel in charge of it says: 'O Lord, male or female? Wretched or happy? Short or tall? Deficient or excessive in his strength and his lifespan? Healthy or sick?' He said: 'So he writes all of that.'" A man from the people said: "Then what is the purpose of deeds, when all of this has already been finished?" He said: "Work, for everyone will be directed toward that for which he was created."