If a man dies and leaves behind a father and children, how is the estate divided?

If a man
dies and he has a father who is still living and male children, or male and
female children, then the father gets one-sixth of the estate, the wife gets
one-eighth if he has a wife, then the rest is given to the children, with
each male getting the share of two females. 

But if the
children are females only, one daughter or more, then the wife takes
one-eighth, if there is a wife then the daughter or daughters take what
Allaah has allocated to them: half for one daughter, and two-thirds for two
or more daughters. Then in addition to the one-sixth, the father takes
whatever is left of the estate after the wife and daughters take their
shares. 

This is
indicated by the words of Allaah (interpretation of the meaning): 

“Allaah
commands you as regards your children’s (inheritance): to the male, a
portion equal to that of two females; if (there are) only daughters, two or
more, their share is two-thirds of the inheritance; if only one, her share
is a half. For parents, a sixth share of inheritance to each if the deceased
left children”

[al-Nisa’
4:11]

Ibn Qudaamah
(may Allaah have mercy on him) said: 

There are
three scenarios with regard to inheritance for the father: 

1 – He
inherits a stipulated share, if there is a son or grandson. He gets no more
than one-sixth and the rest goes to the son and those who are with him. We
do not know of any difference of scholarly opinion concerning this. That is
because Allaah says (interpretation of the meaning): 

“For
parents, a sixth share of inheritance to each if the deceased left children”

[al-Nisa’
4:11]

2 – The
father inherits by virtue of kinship on the male side only. This applies if
there is no child (child includes both male and female). In this case he
takes the wealth if he is the only heir. If there is another heir who is
entitled to a stipulated share, such as a wife, mother or grandmother, then
those who are entitled to stipulated shares are given their shares, and the
rest of the wealth goes to him, because Allaah says (interpretation of the
meaning): 

“if no
children, and the parents are the (only) heirs, the mother has a third”

[al-Nisa’
4:11]

So the
inheritance is given to both parents, then the mother is allocated
one-third, therefore the rest is for the father. 

3 – Where
both the stipulated share and the kinship on the male side are combined.
This is when there are female children, or a son of his son (i.e., along
with the daughter or daughter of his son). In this case, the father gets
one-sixth, because Allaah says (interpretation of the meaning): 

“a sixth
share of inheritance to each if the deceased left children”

[al-Nisa’
4:11]

The father
gets one-sixth if there is a daughter, according to scholarly consensus,
then he takes whatever is left by virtue of kinship on the male side,
because of the report narrated by Ibn Abbaas who said: The Messenger of
Allaah (peace and blessings of Allaah be upon him) said: “Give the
shares of inheritance to those who are entitled to them, and whatever is
left is for the closest male relatives.” Agreed upon. 

The father
is the closest male relative after a son and grandson, and the scholars are
agreed upon all of this. There is no difference of opinion concerning it as
far as we know, praise be to Allaah. End quote from al-Mughni
(6/169). 

And Allaah
knows best.