Allaah Most High says (which means): Then there has succeeded them a generation which has given up prayers (i.e, made their praycrs to be lost, either by not offering them at all or by not offering them perfectly or by not offering them in their proper fixed times, etc.) and have followed lusts. So they will be thrown in Hell. Except those who repent and believe in the Oneness of Allaah and His Messenger (), and act righteously. [Maryam, 19:59-60]
And He (T) said (which means): Woe unto those performers of prayers (hypocrites) who are unmindful of their prayers (i.e., delay their prayer from its stated fixed time). [Al-Maa'oon, 107:4-5]
And He (T) said (which means): O you who believe! Let not your properties or your children divert you from the remembrance of Allaah. And whosoever does that, then they are the losers. [Al-Munaafiqoon, 63:9]
The commentators of the Qur'aan say: "The 'remembrance of Allaah' mentioned in these Aayaat means the five daily prayers. If anyone is so busy in buying and selling, or with his daily work of earning a livelihood, or with his children, that he cannot perform prayers on time, he will be among the losers."
The first thing which will be judged among a man's deeds on the Day of Resurrection is the Prayer. If this is in good order then he will succeed and prosper but if it is defective then he will fail and will be a loser. [Nasaa'ee, Tirmidhee, Ibn Maajah]
Informing us about the inhabitants of Hell, Allaah Most High says (which means): (The people in Hell will be asked:) What has caused you to enter Hell? They will say: We were not among those who used to pray. Nor did we feed the poor. And we used to talk falsehood (all that which Allaah hated) with vain-talkers. And we used to belie thc Day of Recompense. Until there came to us that which is certain (i.e., death). So no Intercession of intercessors will benefit them [Al-Muddaththir, 74:42-48]
The Prophet said (which means): The covenant between us and them is prayer, so if anyone abandons it he has become a disbeliever. [Ahmad, Tirmidhee, Nasaa'ee]
And he also said (which means): What lies between a man and disbelief is the abandonment of prayer. [Muslim, Aboo Dawood, Nasaa'ee]
And he said (which means): If anyone abandons prayer deliberately then he has no claim upon Allaah. [Ibn Maajah, ADAB-AL-MUFRAD of Bukhaari, Tabaraani]
And he said (which means): I have been ordered to fight against the people until they testify that there is no one worthy of worship but Allaah and that Muhammad is the Messenger of Allaah and until they perform the Prayers and pay the Zakaah, and if they do so they will have gained protection from me for their lives and property, unless [they do acts that are punishable] in accordance with Islaam, and their reckoning will be with Allaah Most High. [Bukhaari, Muslim]
And he , mentioning the prayer, said (which means): If anyone keeps to it, it will be light, evidence and salvation for him on the Day of Resurrection. But if anyone does not keep to it, it will not be light, evidence and salvation for him on the Day of Resurrection, and on that Day he will be associated with Qaroon, Pharaoh, Namaan and Ubayy bin Khalaf (an enemy of Islaam from among the Quraysh). [Ahmad, Tabaraanee, Ibn Hibbaan]
Ibn Al-Qayyim explained: The person who abandons prayer will be raised with such a foursome because his neglect of player may be due to his involvement with his property, his country, his administrative work or his trade. Therefore, if he was involved with his property he will be ressurected with Qaroon; if with his country, then with Pharaoh; if with his administrative work, then with Hamaan; and if with his trade then with Ubayy bin Khalaf, the trader among the disbelievers of Makkah.
Ibn Hazm writes conclusively: "It has come from `Umar, `Abdur-Rahmaan bin `Awf, Mu`aadh bin Jabal, Aboo Hurayrah and other companions that anyone who skips one obligatory prayer until its time has finished becomes an apostate. We find no difference of opinion among them on this point."
This was mentioned by Al Mundhiree in AT-TARGHEEB WA AT-TARHEEB. Then he comments: A group of Companions and those who came after them believed that an intentional decision to skip one prayer until its time is completely finished makes one an unbeliever. The people of this opinion include `Umar bin Al-Khattaab, `Abdullaah bin Mas`ood, `Abdullaah bin `Abbaas, Mu`aadh bin Jabal, Jaabir bin `Abdullaah and Aboo Ad-Dardaa'. Among the non-companions who shared this view were: Ibn Hanbal, Ishaaq bin Rahwayh, `Abdullaah bin Mubaarak, An-Nakha`ee, Al-Hakam bin `Utaibah, Aboo Ayyoob As-Sakhtiyaanee, Aboo Dawood At-Tiyaalisee, Aboo Bakr bin Aboo Shaybah, Zuhayr in Harb, and others.