It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Journeys are not to be undertaken except to three mosques: al-Masjid al-Haram, the Mosque of Madinah, and the Mosque of Bayt al-Maqdis (Jerusalem)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13226