Sunan Abi Dawud

‘Abd Allah b. ‘Amr b. al-As reported the Messenger of Allah (May peace be upon him) as saying:when you hear the mu'adhdhin repeat what he says, invoke a blessing on me, for everyone who invoke one blessing on me will receive ten blessings from Allah. Then ask Allah to give me the wasilah, which is a rank in paradise fitting for only one of Allah’s servants, and I hope that I may be the one. If anyone asks Allah that I be given the wasilah, he will be assured of my intercession