Musnad Abu Ya'la al-Mawsili 42:194

On the authority of Abu Sa'id, the Messenger of Allah (may Allah bless him and grant him peace) said: "Do not undertake a journey except to three mosques: the Sacred Mosque (Masjid al-Haram), the Mosque of Medina (Masjid al-Nabawi), and the Furthest Mosque (Masjid al-Aqsa)."