Musnad Ahmad 30:480

'Abd al-Razzaq narrated to us, Sufyan informed us, from Layth, from Ka'b, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When you invoke blessings upon me, then ask Allah for the *Wasilah* for me." It was said: "O Messenger of Allah, and what is the *Wasilah*?" He said: "The highest degree in Paradise, which only one man shall attain, and I hope that I am he."