Sahih Muslim Book 7, Hadith Number 3218.

Chapter : Do not undertake journey (purely for visit to the sacred places) but to three mosques.

Abu Huraira (Allah be pleased with him) reported it directly from Allah’s Apostle (may peace be upon him) that he said: Do not undertake journey but to three mosques: this mosque of mine, the Mosque of al-Haram and the Mosque of Aqsa (Bait al-Maqdis).