Sahih Bukhari Volume 008, Book 077, Hadith Number 594.
Narated By Anas bin Malik : The Prophet said, "Allah puts an angel in charge of the uterus and the angel says, 'O Lord, (it is) semen! O Lord, (it is now) a clot! O Lord, (it is now) a piece of flesh.' And then, if Allah wishes to complete its creation, the angel asks, 'O Lord, (will it be) a male or a female? A wretched (an evil doer) or a blessed (doer of good)? How much will his provisions be? What will his age be?' So all that is written while the creature is still in the mother's womb."