Four Rules of Tawheed
Shaikh Muhammad Bin Abdul Wahhaab
Almighty God, Lord of the Glorious Throne, I pray that He may guide you in this world and the next; that He may always bless you; that He may make you one of those who recognize His bounty, who remain firm in face of adversity, and who repent and seek His forgiveness if they disobey or sin. These three characteristics are the indices of felicity and blessedness.
Know that pure worship and monotheism, which is the religion of Abraham, consists of worshipping God alone, of dedicating yourself sincerely to serving Him. God said: "I have not created jinn and men but to worship Me" . Once you know that God has created you to serve Him, you will realize that there can be no service except with Pure Monotheism (Arabic: Tawhid ). Just as there is no formal prayer without purity, and there is no purity with uncleanliness, so there is no worship of God while worshipping others along with Him (Arabic: Shirk ). By associating others with Almighty God, man's worship is spoilt, his deeds are vain and he is doomed to eternal Hellfire. If you are cognizant of all this, you will realize that your most important care should be to have all the knowledge pertinent thereto, that God may save you from Hell's terrible abyss. Almighty God said: "God will not forgive any the association of anything with Him; but He will forgive any lesser offense to whomsoever He chooses" . Such pertinent knowledge consists of four basic rules, elaborated in Almighty God's Holy Book.
The first rule is the knowledge that the unbelieving pagans whom the Prophet Muhammad, the peace and grace of God be upon him, opposed, did acknowledge that Almighty God - May He be glorified - is indeed the Creator, Provider and Maker of this world. However, this did not make them Muslims. Evidence therefore is in the verse: "Ask them: 'Who sends down for you your provision from the sky and grows it out of the earth? Who hears your prayer and sees your condition? Who brings the living out of the dead and the dead out of the living? Who directs the course of the world?' They will answer: 'God.' Answer: 'Would you then not fulfill your duty to Him?'" 
The second rule is to know that the unbelievers claim that they do not pray to their objects of worship and call on them except to the end that they may intercede on their behalf with God, as the verse said: "Those who worshipped others as patrons beside God, claiming that they did so only to come through their intercession nearer to Him, will receive the judgment of God in the matter they contend. God will not guide the ingrate, the liar" . Evidence regarding intercession is in the verse: "They serve beside God beings which can neither benefit nor harm, claiming, 'These are our intercessors with God.'"  There are two kinds of intercession, one illegitimate and the other legitimate. The former is that which is sought from sources other than God regarding matters where all the power lies in God alone. Evidence for this is-in the verse: "O men who believe, spend of that which We have provided for you before the Day when there will be neither sale nor purchase, neither favors nor intercession. The unbelievers are themselves unjust."  The legitimate intercession is that which is asked of Almighty God, where the intercessor receives his power from Him, and the interceded for is he whom God is pleased to accept as such for his word and deed. Almighty God said: "No one may intercede with God except by His permission" .
The third rule is the knowledge that the Prophet Muhammad, may God bless him and give him peace, appeared among people of many religious traditions. Some worshipped angels; others worshipped the prophets and saints of God; others worshipped trees and stones, sun and moon. All of these peoples were fought by him, as they must, relentlessly without distinction. Evidence therefor is in the following Qur'anic verses: "And fight them, that there may be no aberration in religion, and all religion belongs to Almighty God" . "Day and night, sun and moon, are His creation and sign. Do not .worship the sun or the moon, but God, their Creator, if you seek the truth" . "Almighty God does not command you to take the angels and prophets as Lords" . "And God said to Jesus, son of Mary: 'Did you ask men to take you and your mother for objects of worship beside Almighty God?' He answered: 'Praise be to You, O God! How can I have asked that which is not mine to ask? If I did, You know it and all that is in my mind. I do not know what is in Your mind, O Transcendent, All- Knowing God! I have not conveyed to them except what You have commanded me to convey, namely, Worship and serve God, my and your only Lord. I was a witness for You in their midst. When You caused me to die, You took over the witnessing on them as well as on all else. If You punish them, they are Your creatures; and if You forgive them, You are the Mighty, the Wise" . "Those unto whom they pray [i.e., the saints] themselves seek an avenue to their Lord's mercy, compete in coming close to Almighty God, and fear His punishment. Punishment of your Lord is certainly to be shunned" . "Have you considered al-Lat, al-'Uzza and the third one Manat?  Are yours the males and His the females? Is this not ridiculous? All of them are but names which you have named, following the example of your ancestors. God gave no voucher for them. You follow but a guess and your own desires" .
The people who associate partners with Almighty God, in both belief and worship, in our own day are worse and hence more guilty than those of pre-Islamic times. For, the ancient ones used to only worship others besides God in prosperity and return to genuine faith in adversity, whereas the present day associationists are constant in their unbelief, regardless of prosperity or adversity. Evidence for this is in the Qur'anic verse: "And when they ride in barks [in stormy seas] they address their prayers to Almighty God in complete sincerity, but relapse into shirk (i.e. associating partners with Him) when they reach the shore" . May the peace and blessings of Almighty God be upon Muhammad, his Companions and all those who follow him until the Last Day.
-  Qur'an 51:56.
-  Qur'an 4:47, 115. It should be mentioned that Almighty God will forgive those who have ascribed partners Him, or worshipped others along with Him, if they repent from doing it before they die.
-  Qur'an 10:32.
-  Qur'an 39:3.
-  Qur'an 10:18.
-  Qur'an 2:254.
-  Qur'an 2:55.
-  Qur'an 2:193.
-  Qur'an 41:37.
-  Qur'an 3:80.
-  Qur'an 5:116-118.
-  Qur'an 17:57.
-  The names of false gods which were worshipped by the pre-Islamic Arabs.
-  Qur'an 53:19-23.
-  Qur'an 29:65.