In fact...
In fact, the punishment of the woman is postponed till after the delivery and weaning of the child, to protect him from harm. By the way, you have used the phrase 'for the mother's offence'. Fornication or adultery is not a one person's offence. It needs a man and woman together to make them fornicators. The man who put that child into the womb of the woman is equally criminal. The punishment of fornication and adultery differs according to the marital status of the man and woman.
It ranges from 100 strokes to the stoning to death. Question: According to Sunnis, a dead body may be taken out of the grave if he is buried with some money or gold. But 'Sauti ya Bilal' (Vol.III no. 5) shows that Imam Husain was buried with gold. Is this not bad or was it done purposely? Answer: Imam Husain (a.s.) is not buried with gold. The dome above his grave (a photo of which was published in Sauti ya Bilal, Vol. Ill No. 4) is covered with gold.
Question: I think the purpose behind the rule of 'Idda' period is to ascertain that the woman does not go with a child in her womb who belongs to her late husband and thus gives the child to the new husband. Can't we use scientific means to find out whether the widow has a child in her womb or not ? For, it is very hard to the widows and worries wives much when their husbands fall ill.
Answer: Islam is the universal religion, meant for all mankind - scientists and illiterates, so-called civilized ones and bush-dwellers - to be practised everywhere and in all circumstances. It is not a 'scientists' club.' That is why its rules and regulations have been made by Allah in such a way that a Nomad of Arabia, an Eskimo of Greenland and a pigmy of the Central part of Africa can follow it with equal ease.
That is the reason behind adopting lunar calendar, and prescribing the prayer-times by positions of the sun etc. . . . And that is the reason of prescribing a certain period of 'Idda' (3 months in case of divorce, 4 months 10 days in case of the death of the husband) in which the woman cannot marry another husband.
I do not think any woman, at the approach of the death of her husband, would be worried of not being able of marrying another husband for a short period of 4 months 10 days, instead of grieving for her beloved present husband who is about to depart from this world. As for the scientific methods : How many women can get themselves scientifically examined?