Aslul-Islam (the foundation of Islam) with which a person enters into Islam is known by the following 7 things:
1. The foundation of Islam is known through the agreement of the religions regarding it.
The Exalted said:
وَمَا أَرْسَلْنَا مِنْ قَبْلِكَ مِنْ رَسُولٍ إِلَّا نُوحِي إِلَيْهِ أَنَّهُ لَا إِلَهَ إِلَّا أَنَا فَاعْبُدُونِ
”And we have not sent any messenger before you, except that we inspired him that none is worthy of worship except Me (Allah) so worship me.”
And the Exalted said:
شَرَعَ لَكُمْ مِنَ الدِّينِ مَا وَصَّى بِهِ نُوحًا وَالَّذِي أَوْحَيْنَا إِلَيْكَ وَمَا وَصَّيْنَا بِهِ إِبْرَاهِيمَ وَمُوسَى وَعِيسَى أَنْ أَقِيمُوا الدِّينَ وَلَا تَتَفَرَّقُوا فِيهِ
”He has ordained for you of religion what He enjoined upon Nuh and that which We have revealed to you, (O Muhammad), and what We enjoined upon Ibrahim and Musa and ‘Isa – to establish the religion and not be divided therein.” (Ash-Shura 42:13)
And Nuh said:
وَأُمِرْتُ أَنْ أَكُونَ مِنَ الْمُسْلِمِينَ
”And I have been ordered to be among the muslims.” (Yunus 10:72)
And regarding Ibrahim:
إِذْ قَالَ لَهُ رَبُّهُ أَسْلِمْ قَالَ أَسْلَمْتُ لِرَبِّ الْعَالَمِينَ
”When his Lord said to him: Submit yourself (become muslim). He said: I have submitted to the Lord of the worlds (as a muslim).” (Al-Baqarah 2:131)
And Ibrahim and Ya’qub adviced their sons:
فَلَا تَمُوتُنَّ إِلَّا وَأَنْتُمْ مُسْلِمُونَ
”So do not die except when you are muslims.”
And regarding Musa:
يَا قَوْمِ إِنْ كُنْتُمْ آَمَنْتُمْ بِاللَّهِ فَعَلَيْهِ تَوَكَّلُوا إِنْ كُنْتُمْ مُسْلِمِينَ
”O my people. If you have believed in Allah then put your trust in Him if you are (really) muslims.”
And Al-Hawariyun said to ’Isa:
آَمَنَّا بِاللَّهِ وَاشْهَدْ بِأَنَّا مُسْلِمُونَ
”We believe in Allah, so bear witness that we are muslims.” (Ali ‘Imran 3:52)
Ibn Taymiyyah said:
والإسلام هو دين جميع الأنبياء والمرسلين ومن تبعهم من الأمم كما أخبر الله بنحو ذلك في غير موضع من كتابه فأخبر عن نوح وإبراهيم وإسرائيل عليهم السلام أنهم كانوا مسلمين وكذلك اتباع موسى وعيسى عليهما السلام وغيرهم، والإسلام هو أن يستسلم لله لا لغيره فيعبد الله ولا يشرك به شيئا ويتوكل عليه وحده ويرجوه ويخافه وحده ويحب الله المحبة التامة لا يحب مخلوقا كحبه لله… فمن استكبر عن عبادة الله لم يكن مسلما، ومن عبد مع الله غيره لم يكن مسلما.
”And Islam is the religion of all the prophets and messengers and whoever followed them from the nations, just as Allah has informed about this many places in His Book. He informed about Nuh, Ibrahim, Israeel – may peace be upon them – that they were muslims. And likewise the followers of Musa and ‘Isa – may peace be upon both of them – and others than them. And Islam is that you surrender to Allah and not to others than Him, so you worship him and do not commit shirk to Him in anything. And you put your trust in Him alone, hope for Him and fear Him alone, and you love Allah with a complete love and you don’t love anything from the creation the same way you love Allah… So whoever is too arrogant to worship Allah he is not a muslim. And whoever worships anyone else than Allah with Allah he is not a muslim.”
(Kitab An-Nabawi, p. 127)
2. It is known through the fact that it is the first obligation, due to the hadith from Ibn ’Abbas – may Allah be please with both of them – that the Messenger of Allah – may Allah’s peace and blessings be upon Him – when he sent Mu’adh to Yemen he said to him:
إنك تأتي قوماً من أهل الكتاب فليكن أول ما تدعوهم إليه شهادة أن لا إله إلا الله – وفي رواية: إلى أن يوحدوا الله
“You will verily come to a people from the people of the book, so let the first thing you invite them to be the testimony of ‘There is none worthy of worship except Allah’ – and in another version – that they single out Allah (in worship).”
Narrated by both (Al-Bukhari and Muslim)
3. That it is the first thing which is demanded from a person due to the hadith:
أمرت أن أقاتل الناس حتى يشهدون أن لا إله إلا الله وأن محمدا رسول الله… الحديث
”I have been ordered to fight the people until they bear witness that ‘There is none worthy of worship except Allah and that Muhammad is the Messenger of Allah…’” until the rest of the hadith.
And the foundation of Islam is known through what was the first thing of Islam. The Exalted said:
يَاأَيُّهَا الْمُدَّثِّرُ (1) قُمْ فَأَنْذِرْ (2) وَرَبَّكَ فَكَبِّرْ (3) وَثِيَابَكَ فَطَهِّرْ (4) وَالرُّجْزَ فَاهْجُرْ
”O you enveloped (in garments). Arise and warn. And magnify your Lord. And purify your garments. And keep away from Ar-Rujz (the idols).” (Al-Muddathir 74:1-5)
4. That it is what was in the time of Makkah and those who performed hijrah to Al-Habasha were upon this.
Ibn Taymiyyah said:
واتفقت الأنبياء على أنهم لا يأمرون بالفواحش ولا الظلم ولا الشرك ولا القول على الله بغيرعلم
“And the prophets have agreed upon that none of them have ordered al-fawahish (great evil sins), injustice, shirk and speaking about Allah without knowledge.” (Kitab An-Nabawat p. 430)
And he also said i Al-Fatawa (14/470-471):
إن المحرمات منها ما يُقطع بأن الشرع لم يُبح منه شيئا لا لضرورة ولا غير ضرورة كالشرك والفواحش والقول على الله بغير علم والظلم المحض، وهي الأربعة المذكورة في قوله تعالى
”Verily is there among the forbidden things some things about which there is certainty that the law have never allowed any of these, not in case of necessity nor something else than necessity, such as shirk, al-fawahish, speaking about Allah without knowledge and clear injustice.
And these are the four mentioned in His the Exalted’s words:
قُلْ إِنَّمَا حَرَّمَ رَبِّيَ الْفَوَاحِشَ مَا ظَهَرَ مِنْهَا وَمَا بَطَنَ وَالإِثْمَ وَالْبَغْيَ بِغَيْرِ الْحَقِّ وَأَنْ تُشْرِكُوا بِاللَّهِ مَا لَمْ يُنَزِّلْ بِهِ سُلْطَانًا وَأَنْ تَقُولُوا عَلَى اللَّهِ مَا لا تَعْلَمُونَ
”Say: ‘My Lord has verily forbidden al-fawahish (great evil sins) – what is apparent of them and what is concealed – and sin, and oppression without right, and that you associate as partners with Allah that for which He has not sent down authority, and that you say about Allah that which you do not know.’” (Al-A’raf 7:33)
فهذه الأشياء محرمة في جميع الشرائع وبتحريمها بعث الله جميع الرسل ولم يُبح منها شيئا قط ولا في حال من الأحوال ولهذا أنزلت في هذه السورة المكية
So these things are forbidden in all of the legislations (of the messengers) and Allah has sent all the messengers with the forbiddance of these things. None of these things have ever been allowed, not under any circumstances or in any situations. Due to this it was revealed in a Makki chapter.”
The Messenger of Allah verily stayed in Makkah inviting to tawhid for ten years according to the agreement of the people of sirah (Islamic history) and others than them. Also in each and every Makki chapter is the foundation of Islam mentioned
5. That which a person is asked about in the grave. It is narrated from Al-Bara bin Azib from the Prophet – sallAllahu alayhi wa sallam – that he said:
يثبت الله الذين آمنوا بالقول الثابت قال نزلت في عذاب القبر فيقال له من ربك فيقول ربي الله ونبي محمد صلى الله عليه وسلم
يُثَبِّتُ اللَّهُ الَّذِينَ آَمَنُوا بِالْقَوْلِ الثَّابِتِ
“Allah keeps firm those who believe, with the firm word.” (Ibrahim 14:27)
He said: “This was revealed regarding the punishment in the grave. It will be said to him: ‘Who is your Lord’, so he will say: ‘My Lord is Allah and my prophet is Muhammad – sallAllahu alayhi wa sallam.’”
Narrated by both (Al-Bukhari and Muslim)
6. That shirk is from that which is impossible that Allah would legislate. The Exalted said:
لَوْ كَانَ فِيهِمَا آَلِهَةٌ إِلَّا اللَّهُ لَفَسَدَتَا
”If there in these two (the heaven and the earth) has been other gods then Allah, then they would verily be destroyed.” (Al-Anbiya 21:22)
And that which is not possible this cannot only be concluded through the law, rather it is repulsive in it (the law), the fitrah and the intellects and then it is impossible that the Shari’ah would come with it.
(Al-Minhaaj s. 279 and 295)
7. It does not differ.
Taken and translated from the book “Aslu Din Al-Islam wa huwa At-Tawhid war-Risalah” compiled by Ali bin Khudayr hafizahullah.