Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "Ask Allah Almighty for al-Wasilah for me, for any servant who asks for it for me in this world, I will be a witness and an intercessor for him on the Day of Resurrection."
Imam al-Tabarani recorded this narration in al-Mu'jam al-Awsat. Its chain contains a narrator, al-Walid bin Abd al-Malik al-Harrani, whom Ibn Hibban mentioned in his book al-Thiqat, and he stated that he is mustaqim al-hadith (sound in hadith) when he narrates from thiqah (trustworthy) narrators. (Allamah al-Haythami says:) I say: He narrated this from Musa bin A'yan, and he is thiqah (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 1880
Hadith Gradingمحدثین:إسنادہ حسن۔
Hadith Takhrij«المعجم الاوسط للطبراني باب الالف من اسمه احمد 639 ، أخرجه المعجم الأوسط للطبراني برقم: 637، وأخرجه الأحاديث المختارة برقم: 96»