The Cow - 2:235
There is no sin on you for informing them of your proposal of marriage, or for keeping this intention within you. Allah knows what you think about them. Do not meet them in secret except for the purpose of talking to them in a proper and virtuous manner. And do not attempt to marry them before their waiting period has expired. Know that Allah knows what is in you, so beware of Him. And know that Allah is Forgiving, Compassionate.
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.