Shaykh al-Islaam Ibn Taymiyyah said (Majmoo al-Fataawaa, 1/158-160):

And the mushriks from these (ones) sometimes say: We seek intercession through them, meaning, "We request the angels and the prophets to interced (for us), so when we cme to the grave of one of them we request him to intercede for us, and when we fashion his statue..." - and statues are either in bodily form or as images, just like the Christians form them in their churches - they say, "...our intent behind these statues is to remember those whom they represent and their way (of piety) and we address these statues whilst our intent is to address those people so that they may intercede for us with Allaah." So one of them says,"O honourable master (sayyidee) so and so" or "O my honourable master, George" or "O my honourable master, Peter" or "O my compassionate lady, Mary" or "O my honourable master al-Khaleel" or "Moosaa bin Imraan" and other than that, "...intercede for me with your Lord."

And sometimes they may address the dead person at his grave (saying), "Ask your Lord for me" or they may address the living person who is absent just as they may address him if he was present, alive. And they would recite lines of poetry, one of them saying therein, "O honourable master so and so! I am in your reckoning, I am in your proximity, intercede for me with Allaah, ask Allaah for us that He helps us against our enemy, ask Allaah to remove this hardship (calamity) from us, I complain of such and such to you, so ask Allaah to remove this calamity from us." Or one of them says, "Ask Allaah that He forgives me."

And amongst them are those who interpret His, the Exalted's saying, "If they, when they had been unjust to themselves, had come to you (Muhammad) and begged Allah's Forgiveness, and the Messenger had begged forgiveness for them: indeed, they would have found Allah All-Forgiving, Most Merciful" (4:64), and they say, "When we ask him to seek forgiveness (for us) after his death, we are in the same position as those from the Companions who requested (his) seeking of forgiveness." But through this they oppose the consensus of Companions, those following them in goodness (Taabi'een) and all of the Muslims, for one of them did not ask the Prophet (sallallaahu alayhi wasallam) after his death that he intercede for him and nor did he ask him (the Prophet) for anything and none of the leading Scholars of the Muslims mentioned any of this in their books. Rather it was mentioned by those who mentioned it from the later jurists and they cited narrations fabricated against Maalik (radiallaahu anhu), their mention will come with a detailed discussion about them insha'Allaah.

So these types of address (of speaking) to the angels, prophets and righteous after their death near their graves or in their absence and addressing their statues, are from the greatest types of shirk present with the mushriks besides the People of the Book and also amongst the innovators from the People of the Book and the Muslims who innovated (matters of) shirk and acts of worship for which Allaah, the Exalted, gave no authority. Allaah, the Exalted, said, "Or have they partners with Allah (false gods), who have instituted for them a religion which Allah has not allowed." (42:21)

For supplicating to the angels and prophets after their death or in their absence and asking them and making istighaathah through them and seeking intercession through them in this situation and setting up statues of them - with the meaning of seeking intercession through them (the deceased) - it is from the deen that Allaah did not legislate and with which He did not sent any messenger and with which He did not reveal any book. And it is not obligatory, or recommended by agreement of the Muslims. And none of the Companions or those following them in goodness did this, and nor did any of the leading Imaams of the Muslims command it, even if that is from what is done by many of the people who have their (share) of worship and abstinence, and they bring citations and dreams with respect to it, all of this is from shaytaan.

And amongst them is one who devises poetical compositions (comprising) supplication to the dead, seeking intercessiosn through them and rescue from hardship (istighaathah), or he may mention that in the course of praising the prophets and righteous. All of this is not legislated, nor obligatory and nor recommended by agreement of the Muslims. And whoever worshiped through an act of worship that is not obligatory nor recommended believing that it is obligatory or recommended then he is astray, an innovator with an evil innovation, not a good innovation, by agreement of the leading Imaams of the religion. For Allaah is not worshipped except by what is obligatory or recommended. And many people mention benefits (positive outcomes) about these types of shirk and they use the angle of opinion and (personal) taste as a means of evidence (for these acts), or the angle of taqleed (blind-following) or dreams and what is like this.