Is the word of Tawheed “Laa ilaaha illa Allah Muhammad Rasoolullah” mentioned in the Qur’an?

Firstly:

The key to Islam is the twin declaration of faith (ash-shahaadatayn); no one can enter the religion of Allah except through these words. What is required of him is to utter them, unless he is unable to do so. This is the greatest symbol of Islam, and his faith cannot be valid without it. These two phrases are of the utmost importance in Islam, and none of the Muslims differ concerning that.

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: The twin declaration of faith, the testimony that there is no god worthy of worship except Allah and that Muhammad is the Messenger of Allah, forms the key to Islam, and no one can enter Islam except through these words. Hence the Prophet (blessings and peace of Allah be upon him) instructed Mu‘aadh ibn Jabal (may Allah be pleased with him), when he sent him to Yemen, to let the first thing to which he called them be the testimony that there is no god worthy of worship except Allah and that Muhammad is the Messenger of Allah." (Majmoo‘ Fataawa Ibn ‘Uthaymeen 1/79).

See also the answers to questions no. 703 and 6703 .

Secondly:

The word of Tawheed with this wording, “Laa ilaaha illa Allah Muhammad Rasoolullah,” with the two phrases together in one place, is only mentioned in the Prophet’s Sunnah, as it was narrated by al-Bukhaari (25) and Muslim (22) from Ibn ‘Umar that the Prophet (blessings and peace of Allah be upon him) said: “I have been commanded to fight the people until they bear witness that there is no god worthy of worship except Allah, and that Muhammad is the Messenger of Allah, and they establish regular prayer and pay zakaah. If they do that, then their blood and wealth are protected from me except in cases dictated by Islamic law, and their reckoning will be with Allah.”

Al-Bukhaari (1395) and Muslim (19) narrated from Ibn ‘Abbaas (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) sent Mu‘aadh (may Allah be pleased with him) to Yemen and said: “Call them to bear witness that there is no god worthy of worship except Allah and that I am the Messenger of Allah. If they accept that, then tell them that Allah has enjoined on them five prayers to be offered every day and night. If they accept that, then tell them that Allah has enjoined on them charity (zakaah) to be taken from their rich and given to their poor.”

With regard to the Qur’an, the word of Tawheed is mentioned in it, but the two phrases of the twin declaration of faith do not appear together in one place in the wording that is well known among the Muslims.

The testimony that there is no god worthy of worship except Allah (Laa ilaaha illa Allah) is mentioned in the Qur’an. Allah, may He be exalted, says (interpretation of the meaning):

{So know, [O Muhammad], that there is no god worthy of worship except Allah and ask forgiveness for your sin and for the believing men and believing women} [Muhammad 47:19]

{Allah witnesses that there is no god worthy of worship except Him, and [so do] the angels and those of knowledge – [that He is] maintaining [creation] in justice. There is no deity except Him, the Exalted in Might, the Wise} [Aal ‘Imraan 3:18].

With regard to the testimony that Muhammad is the Messenger of Allah in the Qur’an, Allah, may He be exalted, says (interpretation of the meaning):

{Say, [O Muhammad], “O mankind, indeed I am the Messenger of Allah to you all, [from Him] to whom belongs the dominion of the heavens and the earth. There is no god worthy of worship except Him; He gives life and causes death.” So believe in Allah and His Messenger, the unlettered prophet, who believes in Allah and His words, and follow him that you may be guided} [al-A‘raaf 7:158]

{O you who were given the Scripture, believe in what We have sent down [to Muhammad], confirming that which is with you …} [an-Nisa’ 4:47].

Shaykh ‘Abd ar-Rahmaan as-Sa‘di (may Allah have mercy on him) said: Here Allah, may He be exalted, instructs the People of the Book, the Jews and Christians, to believe in the Messenger Muhammad (blessings and peace of Allah be upon him) and what Allah sent down to him of the great Qur’an.”" (Tayseer al-Kareem ar-Rahmaan fi Tafseer Kalaam al-Mannaan  p. 181).

The place where it is most clearly mentioned is the verse in which Allah, may He be exalted, says (interpretation of the meaning):

{Muhammad is the Messenger of Allah } [al-Fath 48:29].

Similar to that is the verse in which He, may He be exalted, says (interpretation of the meaning):

{Muhammad is not the father of [any] one of your men, but [he is] the Messenger of Allah and last of the prophets. And ever is Allah, of all things, Knowing } [al-Ahzaab 33:40].

And Allah knows best.