Form of the shahaadah that should be recited by an apostate in order to return to Islam
Question

I have question about shahada. I know there are many different ways for non muslim to recite shahada and become muslim. But my question is does a person who is already Muslim and then he commits major kufr by mocking Islam have to recite different version of shahada. I have heard that he must also add wahhdahu lashareekalahu. If a Muslim commits major kufr by mocking Islam, does he have to say this version of shahada or adding these words are just optional. If he doesn't feel comfortable, then can he say this version of shahada? “Ash hadu alla ilaha illa Allah, wa ash hadu anna Mohammadan abduhu wa rasuluh”. Secondly I wanted to ask that some people say illAllah and some people say illa then take a break and then say Allah while reciting shahada. Which one is correct because I don't know arabic. Thirdly, in this shahada, I have heard some people say illa Allahu, lashareekalahu and rasuluhu and I have also heard some people say illa Allah, lashareekalah and rasuluh. Which one is correct and if both are correct then which is better. Lastly, Is it obligatory to add Wahhdahu Lashareekalahu while reciting shahada during tashahhud in Salah and while reciting shahada after wudu? Did Prophet Muhammad (blessings and peace of Allah be upon him) used to add these words?? Are these words obligatory to add anywhere
Praise be to Allah.Firstly:
What should the apostate say in order to return to Islam?
The ruling on the apostate is the same as the ruling on a disbeliever (kaafir) ; he may return to Islam by saying the shahaadah.
‘Abd ar-Razzaaq narrated in al-Musannaf (10/168-169) from ‘Ubaydullah ibn ‘Abdillah ibn ‘Utbah, that his father said: Ibn Mas‘ood arrested some people of Iraq who had apostatized from Islam, then he wrote to ‘Umar concerning their case. He wrote back saying: Present the religion of truth to them, and the testimony that there is no god worthy of worship except Allah. If they accept that, then let them go, but if they do not accept that, then execute them. Some of them accepted it, so he let them go, and some of them did not accept it, so he executed them.
In terms of the wording of the shahaadah, it is sufficient for him to say: “Ashhadu an laa ilaaha ill-Allah wa anna Muhammadan Rasoolullah (I bear witness that there is no god worthy of worship except Allah and that Muhammad is the Messenger of Allah).” In order for it to be valid, he does not have to add the words “wahdahu laa shareeka lah (alone, with no partner).”
This is indicated by the hadith of Ibn ‘Umar, according to which the Messenger of Allah (blessings and peace of Allah be upon him) said: “I have been commanded to fight the people until they bear witness that there is no god worthy of worship except Allah, and that Muhammad is the Messenger of Allah, and they establish regular prayer and pay zakaah. If they do that, then their blood and wealth are protected from me, except in cases dictated by Islamic law, and their reckoning will be with Allah.” Narrated by al-Bukhaari (25) and Muslim (22).
This is a matter concerning which there is consensus among the scholars.
Ibn al-Mundhir (may Allah have mercy on him) said:
All the scholars from whom we acquired knowledge are unanimously agreed that if the disbeliever says, “I bear witness that there is no god worthy of worship except Allah, and I bear witness that Muhammad is His slave and His Messenger, and that everything that Muhammad brought is true, and I disavow every religion that is contrary to the religion of Islam,” and he is an adult of sound mind, then he becomes a Muslim. End quote from al-Ishraaf (8/75-76).
But if he adds something to it, that is good. It was narrated in the hadith of ‘Ubaadah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: “Whoever says ‘I bear witness that there is no god worthy of worship except Allah alone, with no partner, and that Muhammad is His slave and Messenger, and that ‘Eesa is the slave of Allah and His Messenger, a Word which He bestowed upon Maryam and a soul created by Him, and that Paradise is true and that Hell is true, Allah will admit him to Paradise on the basis of whatever he did of deeds.” Narrated by al-Bukhaari (3435) and Muslim (28).
But it must be noted that uttering the testimony of Tawheed (affirming the oneness of Allah) must be accompanied by sincere belief in the heart and certain faith in what this testimony indicates.
Shaykh Sulaymaan ibn ‘Abdillah ibn Muhammad ibn ‘Abd al-Wahhaab (may Allah have mercy on him) said:
It was narrated that ‘Ubaadah ibn as-Saamit said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever bears witness that there is no god worthy of worship except Allah alone, with no partner, and that Muhammad is His slave and Messenger, and that ‘Eesa is the slave of Allah and His Messenger, a Word which He bestowed upon Maryam and a soul created by Him, and that Paradise is true and that Hell is true, Allah will admit him to Paradise on the basis of whatever he did of deeds.”…
The words “Whoever bears witness that there is no god worthy of worship except Allah” mean: Whoever utters this word, understanding its meaning and acting in accordance with what it implies, both inwardly and outwardly, as is indicated by the verses (interpretation of the meaning): “So know, [O Muhammad], that there is no deity except Allah” [Muhammad 47:19] and “except those who bear witness to the truth on the basis of knowledge” [az-Zukhruf 43:86]. As for uttering these words without understanding their meaning or acting in accordance with what they imply, that is of no benefit, according to scholarly consensus.
End quote from Tayseer al-‘Azeez al-Hameed (p. 51).
Secondly:
It is obligatory for the apostate to repent.
In addition to uttering the word of Tawheed (i.e., the shahaadah), it is obligatory for the apostate to repent from what he did of mocking Islam. Repentance means regretting what he did and resolving not to do it again.
An-Nawawi (may Allah have mercy on him) said:
The scholars said: repentance is obligatory from every sin. If the sin has to do with a matter that is between a person and Allah, may He be exalted, and does not have anything to do with the rights of another human, then there are three conditions that must be met in order for repentance to be accepted:

He must give up the sin.
He must regret what he has done.
He must resolve never to do it again.

If one of these three conditions is missing, his repentance is not valid.
End quote from Riyaadh as-Saaliheen (p. 14).
For more information, please see the answer to question no. 9104 .
With regard to the repentance of the apostate in particular, Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
The basic principle concerning that is that in the case of a disbeliever who has never been a Muslim, it is sufficient for him to recite the twin declaration of faith (ash-shaahadatayn) or – according to the more correct scholarly view – for him to recite the first shahaadah, and tell him that he must believe in the second.
In the case of one who was Muslim before [i.e., an apostate], it is essential for him to repent from that which was the cause of him having been deemed an apostate, along with reciting the twin declaration of faith (ash-shaahadatayn), whether he denied an obligatory duty, or he denied the prohibition of something concerning which there is scholarly consensus that that thing is prohibited, or he denied the permissibility of something concerning which there is scholarly consensus that that thing is permitted, or he gave up praying, and so on.
End quote from ash-Sharh al-Mumti‘ (14/468).
Thirdly:
How to pronounce the shahaadah:
The basic principle regarding how the testimony of Tahweed (the shahaadah) is to be pronounced is that the words should be pronounced all in one go, because its meaning will be completed when one pauses at the end, not in the middle at the word illa (except).
So one should say “Ashhadu an laa ilaaha ill-Allah wa anna Muhammadan Rasoolullah (I bear witness that there is no god worthy of worship except Allah and that Muhammad is the Messenger of Allah), in one breath.
Or one may say “Ashhadu an laa ilaaha ill-Allah,” then pause, then say, “Wa ashhadu anna Muhammadan Rasoolullah.”
Fourthly:
Uttering the phrase “wahdahu laa shareeka lah (alone, with no partner)” after doing wudoo’ or in the tashahhud
Saying the phrase “wahdahu laa shareeka lah (alone, with no partner)” in the tashahhud after doing wudoo’ is Sunnah, because it is mentioned in the hadith, as has been explained previously in the answer to question 45730 .
With regard to saying it in the tashahhud in prayer, there are several valid versions of the tashahhud, in one of which it says “wahdahu laa shareeka lah (alone, with no partner)”; in other versions this phrase is not included. All of that is valid and is proven.
See also the answer to question no. 98031 .
And Allah knows best.