Every Messenger said to his people:

O my people! Worship Allaah alone. You have none other than Him that has the right to be a deity to be worshipped. [Soorah al-A’raaf 7:59]

And there are evidences other than this.

Imaam Ibn Rajab, rahimahullaah , said: “To explain this meaning and to clarify it: When a person says laa ilaaha illallaah, it means, according to him, that none has the right to be deified and worshiped except Allaah. And al-Ilah is the One Who is obeyed and not disobeyed; due to awe and veneration of him, and due to love, fear, hope and reliance upon Him; as well as being the One Who is asked from and is supplicated to. And none of this is correct, except for Allaah the Mighty and Majestic.”

This is why when the Prophet sallallaahu ‘alayhi wa sallam said to the unbelievers of the Quraysh: Say laa ilaaha illallaah. They retorted:

Has he made all the deities into a single Deity to be worshiped [i.e. Allaah]? Indeed, this is something very peculiar! [Soorah Saad 38:5]

They [the unbelievers] understood that this kalimah rendered false the worship of any and every deity and restricted worship to just Allaah alone. And they did not want this. So it is clear that laa ilaaha illallaah, along with its requirement, implies: That Allaah alone should be singled out with worship; and that the worship of other than Him should be abandoned. So when a person says laa ilaaha illallaah, he is proclaiming that it is obligatory to single out Allaah alone with worship, and he is [at the same time] denouncing the worship of other than Him; such as [the worship] of idols; [the dead in the] graves; the pious and righteous.

The falsehood of those who worship the [dead in the] graves, and the likes, can be seen in that they believe laa ilaaha illallaah merely implies the affirmation that Allaah exists, or that He is the Creator and the One Who has the ability to originate or other similar beliefs; or that it just means judgement and sovereignty (haakimiyyah) belong solely to Allaah. They think that whoever holds such beliefs and explains laa ilaaha illallaah in this manner, then they have reached the absolute truth of Tawheed - even if they do what they do as regards worshipping others along with Allaah, or believe in [directing worship to] the dead; drawing closer to them by offering sacrifices to them; making vows to them; ritually walking around and circumambulating (tawaaf) their graves and seeking Divine blessings (tabarruk) from the earth around them! These people are unaware that even the unbelieving Arabs held these beliefs, and they acknowledged and affirmed that Allaah was the Creator Who has the ability to originate. They claimed that they worshiped others along with Him because these [other deities] would bring them closer to Allaah; they did not believe that [these deities] were the actual ones who created, or were the providers of sustenance.

If the meaning of laa ilaaha illallaah were as these people claimed, then there would have been no dispute between the Messenger sallallaahu ‘alayhi wa sallam and between the Mushrikoon, those who worshipped idols and others along with Allaah. Indeed, if the Messenger sallallaahu ‘alayhi wa sallam had just asked them to affirm that Allaah is the One Who has the ability to originate and create, or to affirm that Allaah exists. Or if he asked them to judge in accordance with Allaah’s Prescribed Laws concerning issues of blood, property and rights - whilst remaining silent about the issue of [singling out Allaah alone with] worship - then they would have hastened in responding to the Messenger sallallaahu ‘alayhi wa sallam. However, they were a people who understood that if they were to say laa ilaaha illallaah, they would be affirming the falsity of worshipping idols and that this kalimah was not a mere phrase devoid of meaning.