If prayers have been missed, one of the following three scenarios must apply:
1 – The prayer was missed for a reason such as sleeping or forgetting. In that case it must be made up, because the Prophet (peace and blessings of Allaah be upon him) said: “Whoever forgets a prayer or sleeps and misses it, the expiation for that is to pray it when he remembers.” Narrated by al-Bukhaari, 572; Muslim, 684.
He should offer these prayers in order as enjoined, because of the hadeeth of Jaabir ibn ‘Abd-Allaah, according to which ‘Umar ibn al-Khattaab (may Allaah be pleased with him) came on the day of al-Khandaq after the sun had set, and started cursing the kuffaar of Quraysh and saying, “O Messenger of Allaah, I could hardly pray ‘Asr until the sun had almost set.” The Prophet (peace and blessings of Allaah be upon him) said: “By Allaah, I did not pray it either.” We went to Bat-haan and he did wudoo’ for prayer and so did we, then he prayed ‘Asr after the sun had set, then he prayed Maghrib after that. Narrated by al-Bukhaari (571) and Muslim (631).
2 – He omitted the prayer for a reason but he was not aware of it, such as unconsciousness. In this case the prayer is waived for him and he does not have to make it up.
The scholars of the Standing Committee were asked:
I was involved in a car accident and I stayed in the hospital for three months, where I did not wake up and I did not pray for all that time. Is it waived for me or do I have to make up all the missed prayers?
The prayers during the period mentioned are waived in your case, so long as you were unconscious throughout that period. End quote.
They were also asked:
If a person remains unconscious for a month and does not pray throughout that period, then he regains consciousness after that, does he have to repeat the missed prayers?
He does not have to make up the prayers that he missed during that period, because he comes under the same ruling as one who is insane, and the Pen is lifted from one who is insane (i.e., his deeds are not recorded). End quote.
Fataawa al-Lajnah al-Daa’imah, 6/21
3 – He missed the prayers for no reason. One of two scenarios applies in this case:
Either he denied and refused to accept that they are obligatory. In this case there is no dispute that this is kufr and he has nothing to do with Islam. He has to enter Islam and then do all the duties and obligations of Islam, but he does not have to make up the prayers he missed when he was a kaafir.
Or he did not pray because he was negligent and lazy. In this case the prayers are not valid if he makes them up, because he had no excuse at the time when he missed them. Allaah has enjoined prayers at certain, clearly-defined times, as He says (interpretation of the meaning):
“Verily, As‑Salaah (the prayer) is enjoined on the believers at fixed hours”
And the Messenger (peace and blessings of Allaah be upon him) said: “Whoever does an action that is not part of this matter of ours will have it rejected.” Narrated by al-Bukhaari, 2697; Muslim, 1718.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him) was asked:
I did not pray until the age of twenty-four. Now with every fard (obligatory prayer) I offer another fard. Is it permissible for me to do that? Should I carry on doing that, or is there something else I have to do?
The one who missed prayers deliberately does not have to make them up, according to the correct scholarly view. Rather he has to repent to Allaah, because prayer is the foundation of Islam, and failing to pray is the greatest of sins. In fact, failing to pray constitutes major kufr according to the more correct of the two scholarly opinions, because it is narrated that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The covenant that stands between us and them is prayer; whoever does not pray is a kaafir.” Narrated by Imam Ahmad and the authors of al-Sunan with a saheeh isnaad from Buraydah (may Allaah be pleased with him).
And the Prophet (peace and blessings of Allaah be upon him) said: “Between a man and shirk and kufr there stands his giving up prayer.” Narrated by Imam Muslim in his Saheeh from Jaabir ibn ‘Abd-Allaah (may Allaah be pleased with him). And there are other ahaadeeth which indicate the same thing.
What you have to do is repent sincerely to Allaah by regretting what you have done in the past, giving up not praying, and sincerely resolving not to go back to it. You do not have to make up anything, either with every prayer or otherwise. Rather all you have to do is repent. Praise be to Allaah, whoever repents, Allaah accepts his repentance. Allaah says (interpretation of the meaning):
“And all of you beg Allaah to forgive you all, O believers, that you may be successful”
And the Prophet (peace and blessings of Allaah be upon him) said: “The one who repents from sin is like one who did not sin at all.”
You have to be sincere in your repentance, and take stock of yourself, and strive to offer prayers regularly on time in congregation. And you have to ask Allaah to forgive what you have done, and do a lot of righteous deeds, and be optimistic, for Allaah says (interpretation of the meaning):
“And verily, I am indeed forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them (till his death)”
After mentioning shirk, murder and zina (adultery) in Soorat al-Furqaan, Allaah says (interpretation of the meaning):
“and whoever does this shall receive the punishment.
69. The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace;
70. Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allaah will change their sins into good deeds, and Allaah is Oft‑Forgiving, Most Merciful”
We ask Allaah to guide us and you, to make our repentance sound and help us to remain constant in doing good. End quote.
Majmoo’ Fataawa al-Shaykh Ibn Baaz, 10/329, 330
With regard to making up missed fasts, if you did not fast during the time when you did not pray, then you do not have to make up those fasts, because the one who does not pray is a kaafir in the sense of major kufr that puts him beyond the pale of Islam – as stated above. When a kaafir becomes Muslim, he is not obliged to make up acts of worship that he did not do when he was a kaafir.
But if you did not fast at a time when you were praying, then one of the following two scenarios must apply:
Either you did not form the intention to fast from the night before, and you decided rather that you would not fast. In this case making up the fasts would not be valid in your case, because you failed to do the act of worship at the time prescribed for it by Islam, with no excuse.
Or you started to fast then you broke the fast during the day. In this case you have to make it up, because when the Prophet (peace and blessings of Allaah be upon him) commanded the one who had had intercourse during the day in Ramadaan to offer expiation for that, he said to him: “Fast one day in its stead.” Narrated by Abu Dawood, 2393; Ibn Maajah, 1671; classed as saheeh by al-Albaani in Irwa’ al-Ghaleel, 940.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked about the ruling on breaking the fast during the day in Ramadaan with no excuse. He replied:
Breaking the fast during the day in Ramadaan with no excuse is a major sin, which makes a person a faasiq (disobedient, evildoer) who has to repent to Allaah and make up the day when he broke his fast. I.e., if he fasted then during the day he broke his fast with no excuse, then he has sinned, and he has to make up the day when he broke the fast, because when he started it, it became binding upon him, so he has to make it up, like a vow. But if he did not fast at all, deliberately, with no excuse, then it is most likely that he does not have to make it up, because that will not benefit him at all, for it will never be accepted from him. The basic principle with regard to every act of worship which is to be done at a specific time is that if it is delayed beyond that time with no excuse, it will not be accepted, because the Prophet (peace and blessings of Allaah be upon him) said: “Whoever does any action that is not in accordance with this matter of ours will have it rejected.” And he has transgressed the limits set by Allaah, and transgressing the limits set by Allaah is zulm (wrongdoing), and good deeds are not accepted from the wrongdoer. Allaah says (interpretation of the meaning):
“And whoever transgresses the limits ordained by Allaah, then such are the Zaalimoon (wrongdoers)”
If he had done this act of worship ahead of time – i.e., before the time for it began – it would not have been accepted of him, and by the same token, if he does it after that it will not be accepted from him, unless he has an excuse. End quote.
Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen (19, question no. 45)
What he has to do is repent sincerely from all sins, and perform obligatory duties regularly and on time, and give up evil deeds, and do a lot of naafil deeds and acts of worship.
And Allaah knows best.