Question: If a murtad (an apostate; one who renounced Islam) reconverts to Islam, does he have to make up the salats that he had missed before he became a murtad?
ANSWER
When a murtad becomes a Muslim, he has to make up the acts of worship that he missed while he was a Muslim, for omitting a salat or a fast is a sin and the sin will remain after he becomes a Muslim again. (Durar wa-l Ghurar)

A murtad's all previous acts of worship and earned rewards perish. If he becomes a Muslim again, if he is rich, he has to renew the pilgrimage (hajj). But he does not have to reperform his salats, fasts, and zakats (if he performed them before his apostasy). However, those salats that he omitted before his apostasy will have to be performed. A person's apostasy will not absolve him from the sins he committed before apostasy. (Ethics of Islam)

A murtad does not have to make up those salats that he missed during his apostasy. (Hindiyya)

The book Hindiyya says that he does not have to make up only those salats that he missed during his apostasy. It is understood from this statement that he has to make up the salats that he had missed before he became an apostate.

A person who abjured Islam does not have to make up those salats that he missed during his apostasy or those that he had performed before his apostasy. Only the hajj is excluded from this rule. (Durr-ul-mukhtar)

Hadrat Ibn Abidin, explaining these statements, writes, "He does not have to reperform those that he had performed before his apostasy." It is inferred from this explanation too that he has to make up those that he had missed before his apostasy because this matter is explained clearly in Durar wa-l Ghurar.

Breaking repentance a thousand times
Question: It is claimed, "According to the Qur'an al-karim, if a Muslim renounces Islam and becomes an apostate and afterwards makes repentance and returns to Islam and then renounces Islam again, it is not possible for him to be pardoned even if he repents of it." Is it true?
ANSWER
No, it is not true. The meaning of the Qur'anic verse mentioned is as follows:
(Allah will not forgive or guide to the right path those who believe and then reject, and then again believe and then reject, and thereafter increase their disbelief.) [An-Nisa' 137]

It is not said in this verse that those who make repentance after rejection will not be forgiven. What is said is that those who increase their disbelief, that is, those who continue to disbelieve, will not be forgiven. No matter how many times a person becomes an apostate, he will become a Muslim if he repents of it after each. In other words, even if he has broken his repentance a thousand times, what counts is his last status. Judgment is made according to final result. Hadrat Imam-I Qurtubi stated, “According to this verse, Allah does not forgive those who believed in Musa ‘alaihis-salam and then who became disbelievers because of disbelieving in Uzayr ‘alaihis-salam, and then who believed in Uzayr ‘alaihis-salam and afterwards who became disbelievers because of disbelieving in ‘Isa ‘alaihis-salam, and thereafter who increased their disbelief by rejecting Muhammad ‘alaihis-salam. The meaning of Allahu ta’ala’s statement “… and thereafter [who] increase their disbelief” refers to those who insist on disbelief” (Tafsir al-Qurtubi).