As-Salamu `alaykum wa rahmatullah He has. There are several answers on tawassul at SunniPath.com. The fuqaha of the four schools permitted tawassul; this fact is mentioned in the related answers at SunniPath.com. Mufti Muhammad ibn Adam says in his answer: If by seeking help from the Prophets and pious means making them an intermediary between the seeker and Allah, then there is nothing wrong in seeking their help. Tawassul (using intermediaries in supplication to Allah) through the Prophet (Allah bless him & give him peace), Awliya and righteous believers is permitted, rather recommended according to the four schools of Sunni Islam. (Istighatha: Calling Someone Other Than Allah for Help.)