Dought & clear, - If he apostatized then repented, and he owed prayers, fasts or zakaah before he apostatized, then he must make themup- visit-http://aydnajimudeen.blogspot.com

There is someone who apostatized, and before he apostatized, he had
some prayers and fasts that he had to make up but did not. If he comes
back to Islam, does he still have to make them up, or is everything
erased and does he become like someone who is new in Islam?
Praise be to Allah
Firstly:
If the apostate repents, he does not have to make up prayers or fasts
that he did not do during the time of apostasy, because repentance
erases what came before it.
Shaykh Ibn Baaz (may Allah have mercy on him) was asked:
Does the apostate have to make up prayers and fasts if he comes back
to Islam and repents?
He replied:
He does not have to make them up; whoever repents, Allah accepts his
repentance. If a person does not pray, or he does something that
nullifies Islam, then Allah guides him and he repents, then he does
not have to make them up.
This is the correct scholarly view, because Islam erases that which
came before it, and repentance erases that which came before it.
Allah, may He be glorified and exalted, said:"Say to those who have
disbelieved, if they cease (from disbelief) their past will be
forgiven" [al-Anfaal 8:38]. Here Allah, may He be glorified and
exalted, states that if the disbeliever becomes Muslim, Allah will
forgive him everything that he did in the past.
The Prophet (blessings and peace of Allah be upon him) said:
"Repentance erases that which came before it, and Islam erases that
which came before it."
End quote fromMajmoo' Fataawa Ibn Baaz, 29/196
See also the answer to question no. 197247
Secondly:
But if before he apostatized, the apostate had missed some prayers or
fasts or zakaah, then he must make them up, according to the majority
of scholars.
It says inal-Mawsoo'ah al-Fiqhiyyah(22/201-202):
If the apostate who has repented owed some prayers or fasts or zakaah
that he missed before he apostatized, does he have to make them up?
The majority of Hanafi, Shaafa'i and Hanbali fuqaha' are of the view
that it is obligatory to make them up, because omitting an act of
worship is a sin, and sins remain after apostatizing. End quote.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: In
the case of the apostate, he is not obliged to make up prayers, zakaah
and fasts that he missed during his apostasy, according to the
well-known scholarly view, but he has to make up anything that he
missed before he apostatized, according to the well-known view.
And Allah knows best.