Musnad Ahmad 27:1687

Ya'qub narrated to us, my brother's son of Ibn Shihab narrated to me, from his paternal uncle, Salim ibn 'Abdullah informed me, that 'Abdullah ibn 'Umar informed him, that the Messenger of Allah (may Allah bless him and grant him peace) said: "The Jews will fight you, and you will be given power over them, until the stone says: 'O Muslim, this is a Jew behind me, so kill him.'"