It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "When you hear the mu'adhdhin giving the adhan, say as he says, and send blessings upon me, for whoever sends blessings upon me, Allah sends ten mercies upon him. And ask Allah for al-Wasilah for me, for al-Wasilah is a station in Paradise that befits only one servant among the servants of Allah, and I hope that I will be he. Whoever asks for it for me, my intercession becomes due for him on the Day of Resurrection."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1930