Musannaf Ibn Abi Shayba 27:887

Ibn Numayr narrated to us, from Musa ibn Ubaydah, who said: Yusuf ibn Tahman informed me, from Abu Umamah ibn Sahl ibn Hunayf, from his father Sahl ibn Hunayf, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever performs ablution and perfects his ablution, then comes to the Mosque of Quba and performs four rak'ahs in it, that shall be equivalent to an 'Umrah."