If a Muslim wasn't used to pray and then he started and never left a prayer, does he need to pray all prayers he has previously left or Allah (Subhanahu wa Ta'ala) will forgive him?
According to the majority of scholars, no, he does not need to make them up. This is because none of the companions, tabi'een, etc. ever made them up; there is no explicit ayah of Qur'an, or hadith of rasulullah (peace be upon him) telling us to make up prayers we missed.
In fact, this is a serious issue to consider: A missed prayer cannot be made up, ever. It's missed. Forever. You can see this fatwa on Islam-QA as one reference.
As mentioned in @AlUmmat's answer, he should make tawbah (sincere repentance) for what he did wrong, and move forward by praying on time, every time.
If the issue is someone accidentally skipping a prayer, such as if they set their alarms for Fajr (early morning) prayers and slept through, then the scholars mention that they must make it up as soon as they remember (i.e. wake up enough to realize they missed it). This is from the hadith:
Allah's Messenger said: "Whoever forgets a Salat then he is to pray it when he remembers it." (Sahih) Recorded in At-Tirmidhi
I know it's a quite old question, but in order to help new search:
First, as everyone said it, you must first do a sincere tawabah. Indeed Allah will incha'Allah forgive... But remember that no one is sure that his tawbah is sincere enough, and remember that Allah has said in the Quran (15:49) "Tell My servants that I - I alone - am truly forgiving, a true dispenser of grace;" and just after (15:50) "and [also,] that the suffering which I shall impose [on sinners] will indeed be a suffering most grievous."
نَبِّىءْ عِبَادِي أَنِّي أَنَا الْغَفُورُ الرَّحِيمُ
وَ أَنَّ عَذَابِي هُوَ الْعَذَابُ الأَلِيمَ
Scholars interpret tawbah (repentance) to do all of the following:
- immediate renunciation of the sin
- firm intention and determination to not return to the sin ever again,
- regret over having committed a sin
- compensate for it if the sin was against the rights of another human being (steal something, swear at someone, brake something... Huququl 'ibaad = right of Allah's servant)
One of mark of sincere repentance should not be to try to compensate Huququllah (right of Allah) ? This is why I will suggest you to make up as many days of missed prayers as you can each day. Go at a pace that you can sustain. There's no need to "Qaza Umri" in a few days as it will discourage you (as stated in another answer). You should rather be consistent/steady on a small amount, even one prayer qaza by day.
Another good way to do it is to make up some prayers before you start each prayer for that day.
For more information, i will suggest you to have a look to:
Note: you have to replace missed salah since you became muslim (if you convert to islam) or since bulugh.
In fact a missed prayer cannot be made up, ever. It's missed for forever.
According to the majority of scholars, no, he does not need to make them up. This is because none of the Companions, Tabi'een, etc. ever made them up; there is no explicit ayah of Qur'an, or hadith of Rasulullah (peace be upon him) telling us to make up prayers we missed. Imam Nawawi refers to the hadith related by Anas that the Messenger of Allah (Allah bless him and give him peace) said, “Whoever forgets a prayer must perform it when they remember it…” [Bukhari (597), and Muslim (684).
Prayers missed in life time will only be made up through true and sincere repentance from Almighty Allah Who is Ever Forgiving, Ever Merciful. Qaza Umri for the lifetime missed prayers in reality discourage people from performing prayers due to fear of past guilt. Remember, Allah, the Almighty is so GREAT that HE Forgives all your sins even if you bring a mountain full of your sins, provided you seek forgiveness truly and sincerely from the core of your heart.
In the name of God, the Beneficent, the Merciful
All perfect praise be to God, the Lord of the worlds. I testify that there is none worthy of worship except God and that Muhammad ￼ is His slave and Messenger.
Your question: Does a Muslim have to pray all the prayers that he left out?
Answer: Yes, you can. But you must make a clear intention as follows: “I’m performing such and such day’s Fajr prayer (for example).
If you have missed so many prayers that you don’t remember the exact number of prayers missed then the intention should be made as follows: “oh God! From those prayers I have missed, I am performing the first Fajr Salaah (for example)”. Likewise a person should try to roughly remember how many prayers he/she has to make up for and make up for them as soon as possible until content that all missed prayers are performed.
Why should a person make up his or her lost prayers due to laziness?
Because, no one knows when death will come upon him or her, so better be prepared. Do your homework (by praying, trying to recover the lost prayers, do good etc..) so that you can pass the final exam (the Day of Judgment)
the messenger of God (peace and blessings be upon him) mentions:
Whenever one of you misses a prayer due to sleeping or due to negligence, it is obligatory upon him/her that he/she pray the prayer when he remembers it because God has metioned, “Perform prayer when you remember me”(Muslim,Hadith 1569)
Yes he must pray all left but, of some special cases
But, the other part of your question regarding forgiveness Its absolutely Allah SWT decision that he forgive or punish him.