Musannaf Ibn Abi Shayba 3:5057

Waki' narrated to us, he said: Al-Mas'udi narrated to us, from Al-Qasim ibn 'Abd al-Rahman, from Ibn 'Umar, who said: "If you place the west to your right and the east to your left, then what is between them is the Qibla for the people of the north."