"Verily the creation of everyone of you is brought together in the mother's womb as a drop of semen for forty days, then it becomes a clot for the same period, then it becomes a blob of flesh for the same period. Then the angel will be sent unto it to blow into it a spirit (ruh), and the angel ordered (to carry out) with four instructions: to write down his livelihood, the span of his life, his deeds, and either he is wretched or fortunate..." And so goes the first part of one of the most well-known hadeeth recorded by Bukhari and Muslim on the subject of Qadr (predestination).
The significance of this hadeeth is that science has recently verified this process of embryo/fetus development.