It is narrated from Sayyiduna Sahl bin Hunayf (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever goes out and comes to this mosque (meaning the Mosque of Quba) and prays in it, that is equal to an Umrah."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5537