"From the slave who is poor and in need of Him, the Secretary of Legal Opinions in the city of Hama (Syria) and the Preacher in the Madfan Mosque, to the brother who asked a question, Sayyid ʿAshiq al-Rahman in Wilayatullah Abad in India: Warm greetings and blessings. To proceed: You have asked a question on a legal issue, and this answer is given after some delay because I was away in the Hijaz.
"You asked about <<al-tawassul ilallah taʿala bi al-anbiya' wa al-mursalin>>
-- seeking/using means to Allah the Exalted with/through/by means of the
Prophets and the Messengers -- and about <<hukmu man tawassal>> the law's
position with regard to the person who makes tawassul. This is the answer:
"The Community has reached consensus on the fact that tawassul is permissible when belief is sound (idha sahhat al-ʿaqida), and the consensus of the Community is a legal proof (ijmaʿ al-umma hujjatun sharʿiyya); as the Prophet ﷺ said: "My Community shall not agree on an error." As for the claim of some extremists (ghulat) of the Wahhabiyya whereby the law's position with regard to the person who makes tawassul is that it is shirk (worshipping other than Allah together with Him): there is no proof for such a claim either legally or rationally, because the person who makes tawassul does not contravene the Prophet's order: "If you ask, ask Allah, and if you seek help, seek help from Allah." Rather, he is asking Him through one beloved to Him in order that his supplication be answered, and this is what our Lord Glorious and Majestic likes from us. How then can we judge that he is committing shirk when he is not a mushrik (one who commits shirk). Such a act the law considers abominable and our religion declares itself innocent of it, because it has been said: "Whoever declares a believer to be an disbeliever has committed disbelief."
"Our master Usama ibn Zayd killed a mushrik after the latter had said:
"There is no god but Allah" (la ilaha illallah). When news of this reached
Allah's Messenger ﷺ he condemned our master Usama in the strongest terms
and he said to him:
"How can you kill him after he said La ilaha illallah?"
He replied: "But he said it with the sword hanging over his head?" The
Prophet ﷺ said again: "How can you kill him after he said La ilaha illallah?" He replied: "O Messenger of Allah, he said it in dissimulation (taqiyyatan)" The Prophet ﷺ said: "Did you split his heart open (to see)?" and he did not cease to reprove him until Usama wished that he had not entered Islam until after he had killed that man so that he might have been forgiven all his past sins through belief.
"From this and other narrations we conclude that some of the Wahhabis today may be guilty of hastening to accuse others of disbelief (takfir), as they have done in the past with hundreds of thousands in the Hijaz whom they massacred even as they were saying La ilaha illallah, and as the Kharijis have done in the time of our Master ʿAli -- may Allah ennoble his face.
"In short, tawassul is not prohibited, rather it is legally commendable
(mustahsanu sharʿan), and it is not permitted (la yajuz) to cast the
label of shirk on the believer. This is what will be found in the
established books of Islamic law. And Allah knows best."
Tawassul (supplicating Allah through a means) through a living or deceased intermediary is not the seeking of assistance from a physical body, or through a life or death; rather, it is to seek assistance through the positive meaning attached to the person in both life and death, and due to their rank with Allah, for the body is but the vehicle that carries that significance. ...
Therefore, there is nothing wrong in using the Prophets, saints and the righteous as intermediaries to Allah, through any of the above mentioned means, as long as one does not believe them to have the power to benefit or harm in of themselves without the granting of Allah.--from sunnipath.com , x L 20120703