In the name of Allah, the Beneficent, the Merciful
Prayer is the pillar of the religion, the foremost of good deeds, and the first of actions for which we will be judged on the Day of Resurrection. Therefore, it is an obligation for Muslims to make up for missed prayers as an expiation for being absent during prayer at its fixed time.
Whoever misses a prayer out of honest forgetfulness or sleep or another valid excuse, then his only expiation is to perform that prayer as soon as he remembers. By doing so he will be absolved of any sin for missing the prayer.
Anas ibn Malik reported: The Messenger of Allah, peace and blessings be upon him, said:
مَنْ نَسِيَ صَلَاةً فَلْيُصَلِّهَا إِذَا ذَكَرَهَا لَا كَفَّارَةَ لَهَا إِلَّا ذَلِكَ
Whoever forgets a prayer should pray it when he remembers. There is no expiation other than this.
Source: Sahih Bukhari 572, Grade: Muttafaqun Alayhi
Deliberately missing a prayer is a major sin we must strive to avoid. The scholars disagreed about the expiation for a Muslim who misses a prayer on purpose due to laziness or another invalid excuse. The majority of scholars maintain that he must make up such prayers as far as possible, while a minority of scholars maintain that such prayers will not be valid.
أَجْمَعَ الْعُلَمَاءُ الَّذِينَ يُعْتَدُّ بِهِمْ عَلَى أَنَّ مَنْ تَرَكَ صَلَاةً عَمْدًا لَزِمَهُ قَضَاؤُهَا وَخَالَفَهُمْ أَبُو مُحَمَّدٍ عَلِيٌّ بْنُ حَزْمٍ فَقَالَ لَا يَقْدِرُ عَلَى قَضَائِهَا أَبَدًا وَلَا يَصِحُّ فِعْلُهَا أَبَدًا قَالَ بَلْ يُكْثِرُ مِنْ فِعْلِ الْخَيْرِ وَصَلَاةِ التَّطَوُّعِ لِيَثْقُلَ مِيزَانُهُ يَوْمَ الْقِيَامَةِ وَيَسْتَغْفِرُ اللَّهَ تَعَالَى وَيَتُوبُ
There is a consensus among the reliable scholars that whoever leaves a prayer on purpose must make it up. Ibn Hazm disagreed with them on this and he said such a person cannot ever make them up and they will not be valid. Rather, he said one should increase his good deeds and voluntary prayers in order to make his scales heavy on the Day of Resurrection and he should seek forgiveness from Allah the Exalted and repent.
Source: Majmu’ Sharh Al-Muhadhab 3/79
Ibn Hazm and those who agreed with him maintain that prayers missed without a valid excuse will not be accepted, due to the saying of Allah the Exalted:
إِنَّ الصَّلَاةَ كَانَتْ عَلَى الْمُؤْمِنِينَ كِتَابًا مَّوْقُوتًا
Verily, the prayer is a duty upon the believers at prescribed times.
Surah An-Nisa 4:103
These scholars said that it is not prescribed for a Muslim to make up such prayers, but rather he must compensate by increasing his good deeds, seeking the forgiveness of Allah, and repenting.
Ibn Taymiyyah said:
وتارك الصلاة عمدا لا يشرع له قضاؤها ولا تصح منه بل يكثر من التطوع وكذا الصوم وهو قول طائفة من السلف كأبي عبد الرحمن صاحب الشافعي وداود وأتباعه
It is not legislated for one who leaves the prayer on purpose to make it up and it will not be accepted from him. Rather, he should increase his voluntary good deeds such as fasting. This is the opinion of a group of the righteous predecessors (salaf), such as Abdur Rahman the companion of Ash-Shafi’ee, Dawud, and those who followed them.
Source: Al-Ikhtiyarat 34
In our times, some Muslims lapse in their prayers and they have missed many prayers, sometimes over the course of years. If it is possible for such a person to calculate how many prayers have been missed and to make them up in a reasonable manner, then he should make them up, according to a fixed daily schedule if necessary.
However, if it is not possible to calculate the number of missed prayers or to make them up in a reasonable manner or if such a hardship might deter a person from returning to prayer, then he should increase his good deeds, seek the forgiveness of Allah, and repent.
Success comes from Allah, and Allah knows best.