Musnad Ahmad 32:557

Yunus narrated to us, Hammad—meaning Ibn Zayd—narrated to us, Ubayd Allah ibn Abi Bakr informed us, from his grandfather Anas ibn Malik, who attributed the hadith [to the Prophet], he said: "Indeed, Allah has appointed an angel over the womb. He says: 'O Lord, a drop [nutfah]! O Lord, a clinging clot [alaqah]! O Lord, a morsel of flesh [mudghah]!' Then, when Allah intends to decree its creation, he says: 'O Lord, male or female? Wretched or happy? What is the provision? What is the lifespan?' He said: 'So it is written like that in its mother's womb.'"