Shaikh Muhammad ibn Abdul-Wahhab al-Wasabi (may Allah preserve him).
That the religion of al-Islaam can be summarized into two basic important and mighty principles, and they are as follows:
The First (al-Awwal):
That we do not worship anyone except Allaah alone, having no partner in that
[An-laa Na’budu illa-Allaah Wahdahu laa Shareeka lah].
Allaah (ta’aalaa) said:
Say (O Muhammad (Sallalahi Alaihi wa Sallam): “O people of the Scripture (Jews and Christians): Come to a word that is just between us and you, that we worship none but Allaah, and that we associate no partners with Him, and that none of us shall take others as lords besides Allaah.” Then, if they turn away, say: “Bear witness that we are Muslims.” (Aali Imraan 3:64)
And He (ta’aalaa) said: And your Lord has decreed that you worship none but Him. (Al-Israa’ 17:23)
And this is the meaning of: (I bear witness that none has the right to be worshipped except Allaah) [Ash-hadu an-laa Ilaaha illa-Allaah].
And The Second (ath-Thaanee):
That we do not worship Him except by what He legislated in His Book or in the Sunnah of His Messenger Muhammad (Sallalahi Alaihi wa Sallam), without innovations and desires [An-laa Na’budahu illaa bimaa Shara’ fee Kitaabihi aw fee Sunnati Rasoolihi Muhammad (Sallalahi Alaihi wa Sallam) laa bil-Bida’i wal-Ahwaa’].
He (ta’aalaa) said:
[Say (O Muhammad (Sallalahi Alaihi wa Sallam) to these idolaters (pagan ‘Arabs) of your folk:] Follow what has been sent down unto you from your Lord (the Qur’aan and Prophet Muhammad’s Sunnah), and follow not any Awliyaa’ (protectors and helpers, etc. who order you to associate partners in worship with Allaah), besides Him (Allaah). Little do you remember! (Al-A’raaf 7:3)
And He (ta’aalaa) said:
And whatsoever the Messenger (Muhammad (Sallalahi Alaihi wa Sallam) gives you, take it, and whatsoever he forbids you, abstain (from it), and fear Allaah. Verily, Allaah is Severe in punishment. (Al-Hashr 59:7) And this is the meaning of: (I bear witness that Muhammad (Sallalahi Alaihi wa Sallam) is the Messenger of Allaah) [Ash-hadu anna Muhammadar-Rasool-ullaah].
Shaykhul-Islaam ibn Taymiyyah (rahimahullaah) said in his valuable book ((Iqtidaa’ as- Siraatul-Mustaqeem Mukhaalifat Ashaab al-Jaheem)) [The Requirements of the Straight Path in Opposing the Companions of the Fire] page 451:
( And these two fundamentals: are the essence of the religion (Jimaa’ ad-Deen): That we do not worship anyone except Allaah and that we do not worship Him except with what He has legislated, and we do not worship Him with innovations … and these two fundamentals, they are the realization and the perfection of the two testimonies (ash-Shahaadatayn), which are the head of al- Islaam … ). End of quote. And see at-Tahqeeq wal-‘Eedaah of ash-Shaykh Ibn Baaz (rahimahullaah) page: 63.
EXPLANATION OF THE TEXT BY SHAYKH AHMED AL-WASAABEE (HAFIDHAHULLAAH):
Regarding the first fundamental principle, which is the Tawheed of Allaah, the Shaykh mentioned that in the Kitaab of Allaah and the Sunnah of His Messenger we find many Aayaat and Ahaadeeth that point to this great fundamental principle. And it was for this cause that Allaah (subhaanahu wa ta’aalaa) sent His Messengers, and He ordered them to call the people first and foremost to this fundamental principle, which is the Tawheed of Allaah, and the oneness of Allaah in His worship (Tawheed al-Ulooheeyah), and the oneness of Allaah in His Names and Attributes (Tawheed al- Asmaa was-Sifaat), and the oneness of Allaah in His Lordship (Tawheed ar-Ruboobeeyah).
Allaah (subhaanahu wa ta’aalaa) said:
And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): “Worship Allaah (Alone), and avoid (or keep away from) Taaghoot (all false deities, etc. i.e. do not worship Taaghoot besides Allaah).” (An-Nahl 16:36)
And He (ta’aalaa) said:
And We did not send any Messenger before you (O Muhammad (Sallalahi Alaihi wa Sallam)) but We inspired him (saying): Laa Ilaaha Illaa Ana [none has the right to be worshipped but I (Allaah)], so worship Me (Alone and none else).” (Al-Anbiyaa’ 21:25)
So if a person worships Allaah (subhaanahu wa ta’aalaa) and obeys these commands of Allaah, then this is the realization of Tawheed, and this is the first fundamental which this religion of al-Islaam is based upon.
Regarding the second fundamental principle, and it is that we do not worship Allaah except by what He has legislated in His Book or in the Sunnah of His Messenger Muhammad (Sallalahi Alaihi wa Sallam), and that we do not worship Him with innovations and desires. The Shaykh mentioned that those who beautify and make beautiful to themselves innovations and desires, and from the innovations is celebrating the Mawlid (birthday) of the Prophet (Sallalahi Alaihi wa Sallam), which is an innovation of the Soofiyyah, and the Shaykh mentioned that this is not allowable in our religion and it is not legislated, and the people who perform this, they are under a severe threat. Allaah (subhaanahu wa ta’aalaa) has issued a severe warning against those who oppose and go against the commandments of the Messenger:
And let those who oppose the Messenger’s (Muhammad (Sallalahi Alaihi wa Sallam)) commandment (i.e. his Sunnah legal ways, orders, acts of worship, statements, etc.) (among the sects) beware, lest some Fitnah (disbelief, trials, afflictions, earthquakes, killing, overpowered by a tyrant, etc.) befall them or a painful torment be inflicted on them. (An-Noor 24:63)
We have been ordered to be followers and we have been ordered to take firm hold of the Sunnah. So that which the Prophet (Sallalahi Alaihi wa Sallam) has given us, then it is upon to take it and firmly hold on to it, and that which he prohibited us from then it is upon us to prohibit ourselves from it. And the one who goes against the clear orders of the Messenger (Sallalahi Alaihi wa Sallam) is in opposition to the Messenger, and he is on a great level of jeopardy, and if Allaah (subhaanahu wa ta’aalaa) does not give him the Tawfeeq to repent, and he dies upon this, then he is in a dangerous state. And many of the people in this day and age have fallen into numerous types of innovations, such as the Soofiyyah and the Raafidhah, and other than them. And they have not prohibited themselves from that which the Prophet (Sallalahi Alaihi wa Sallam) has prohibited them from, and they have not enjoined upon themselves that which the Prophet (Sallalahi Alaihi wa Sallam) has enjoined upon them and ordered them with.
And in the valuable book of Shaykhul-Islaam Ibn Taymiyyah is the warning to the Believers of following the path of the people whose destination is the Fire, the people of the Book, the Jews and the Christians. And in this day and age we find many of the Muslims following the Kuffaar in all levels of life. And verily we have been ordered to oppose the Kuffaar in all actions and in all levels of life, such as our speech, and our character, and in our dress, and in our actions of worship, so much so that even in the prayer, as the Prophet (Sallalahi Alaihi wa Sallam) has said: ((Pray in your shoes, for verily the Jews do not pray in their shoes)). A Hadeeth.
And many of the Muslims have invented various holidays following in the footsteps of the Kuffaar, such as labor day, and workers holiday, and mothers day, and other holidays like this, all of which are alien to al-Islaam and all of which are innovations.
Source : Class 43 : May – 13 – 06 of Lessons on Tawhid – Approximately 50 Classes – from Dar-ul-Hadith, Dammaj, Yemen