Musnad Ahmad 27:988

'Ali ibn 'Abdullah narrated to us, Mu'adh ibn Hisham narrated to us, my father narrated to me, from Ayyub, from Nafi', from Ibn 'Umar, that the Prophet of Allah, peace and blessings of Allah be upon him, said: "Whoever is able to die in Al-Madinah, let him do so, for I will intercede for whoever dies in it."