The Cow - 2:228
The divorced women should wait three months for themselves (before marrying another). It is not fitting for them to conceal what Allah has created in their wombs if they believe in Allah and the Last Day. In that case (if they become pregnant) their husbands have more right to take them back if they wish to reconcile. Women have equal rights over men as men have rights over women, and men have a rank over them (in case of pregnancy). Allah is Mighty, Wise.
What is the waiting period for a woman if her husband dies?
The Cow/2:234
The wives left behind by the men who die among you wait four months and ten (days). When they have fulfilled their term, there is no responsibility on you to do what is suitable for them. Allah is All-Knowing of what you do.