Shaikh Saleh al Fawzaan states in his explanation of Kitab at-Tawhid under the chapter [From Shirk is to seek Aid and Assistance (after a calamity befalls) from other than Allah or to Call Upon Others]:
“Indeed Shaikh ul-Islam ibn Tamiyyah mentioned in one of his works – or rather, in many of his works – paraphrased as follows; Indeed that which occurs to the worshippers of graves in terms of their needs being fulfilled [i.e. the affair they seek at the grave actually occurs for them], then that is not an evidence upon the correctness of their methodology [i.e. the methodology of grave worship], because obtaining what is desired is [a means of] trial and test upon them from Allah……so this is not from the beneficial affairs for the grave worshipper, so if something does occur from what they desire then it is [actually] a degradation from Allah upon them…[despite the fact that he may think he is upon the correct methodology and be pleased and therefore continue upon his way believing his request has "apparently" been answered by the dead in the graves that he calls upon!].
Furthermore, Shaikh ul-Islam mentioned also, that it is possible the shayaateen [referring to the devils of jinn in this instance] sometimes take the appearance of the one buried and rise up from the grave in that appearance and speak to the people who are calling upon the dead. They then say to them we will take care of your needs, and they bring them items from far away, they may steal from the items of the people and bring them…and the one who was calling upon the dead thinks this is actually the dead individual himself who has arisen from the grave since the shaytaan has taken that appearance! In reality the actual dead individual does not have the slightest idea of what is occuring above his grave! Rather he is preoccupied with himself, either in blessings or punishments of the grave.
Thereafter, when the people are all raised on the Day of Recompense, those dead individuals on that Day will declare their innocence of the mushrikoon who used to call upon their graves in this World…..”
[Translators Note: For further details on issues of grave worship and seeking intercession etc, an excellent source of information are the various books of Shaikh Mohammad bin Abdul Wahhab, namely Kashf as-Shubuhaat (Exposition of the Doubts), as well as Kitab at-Tawhid, al-Qawaa'id al-arba'a (The Four Fundamental Principles)....exactly the types of books the scholars advise with in the early stages of seeking knowledge].
May Allah place ease into the affair of seeking knowledge, in order that we may remove ignorance from ourselves and others, for indeed the numbers of individuals that have succumbed to the whispers of the Shaytaan in such affairs as mentioned above are of considerable proportions across the World.