see also EMBRYOLOGY.
Narrated Abdullah:Allah's Apostle, the true and truly inspired said, "(as regards your creation), every one of you is collected in the womb of his mother for the first forty days, and then he becomes a clot for an other forty days, and then a piece of flesh for an other forty days. Then Allah sends an angel to write four words: He writes his deeds, time of his death, means of his livelihood, and whether he will be wretched or blessed (in religion). Then the soul is breathed into his body. So a man may do deeds characteristic of the people of the (Hell) Fire, so much so that there is only the distance of a cubit between him and it, and then what has been written (by the angel) surpasses, and so he starts doing deeds characteristic of the people of Paradise and enters Paradise. Similarly, a person may do deeds characteristic of the people of Paradise, so much so that there is only the distance of a cubit between him and it, and then what has been written (by the angel) surpasses, and he starts doing deeds of the people of the (Hell) Fire and enters the (Hell) Fire." (Sahih Bukhari 4.549)
``the minimum period of human gestation after which the child is known to be viable. This is in accordance with the latest ascertained scientific facts.''Campbell comments:
''The verse goes on, ``...At length when he reaches the age of full strength and attains forty years, he says, `O my Lord, grant me that I may be grateful for Thy favor...truly I have repented and truly do I bow in Islam.''Such a statement speaking about 40 years seems to be for every normal man, not for some special circumstance. If the command for nursing is 24 months, a normal period of time; and man reaching 40 years of age is a normal condition; then we would expect the first part of the phrase concerning gestation to be speaking about a usual period of gestation (nine months); and not an unusual period of six months which is really an illness.''
   (William Campbell, The Qur'an and the Bible in the Light of History and Science, Section 4.II.B, Middle East Resources 1992).