Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) relates that the Prophet (peace and blessings be upon him) said: "Whoever, after hearing the adhan, recites these words: 'I bear witness that there is no god besides Allah Almighty, He alone is God, He has no partner, and that Sayyiduna Muhammad (peace and blessings be upon him) is His servant and His Messenger. O Allah, send blessings upon Sayyiduna Muhammad (peace and blessings be upon him), bring him to the rank of al-Wasilah in Your presence, and grant us a share in his intercession on the Day of Resurrection,' (the Prophet (peace and blessings be upon him) said:) intercession becomes due for that person."
Imam al-Tabarani recorded this narration in al-Mu'jam al-Kabir. Its chain contains a narrator, Ishaq bin Abdullah bin Kaysan, whom Imam al-Hakim (may Allah have mercy on him) declared layyin (soft) and Ibn Hibban declared da'if (weak); the remaining narrators of this narration are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 1881