Abu Dawud Book 2, Hadith Number 457.

Narated By Maymunah ibn Sa’d : I said: Apostle of Allah, tell us the legal injunction about (visiting) Bayt al-Muqaddas (the dome of the Rock at Jerusalem). The Apostle of Allah (PBUH) said: go and pray there. All the cities at that time were effected by war. If you cannot visit it and pray there, then send some oil to be used in the lamps.