Musnad Ahmad 27:1649

'Affan narrated to us, Wuhayb narrated to us, Musa ibn 'Uqbah narrated to us, Salim narrated to me that he heard 'Abdullah ibn 'Umar say: The oath of the Messenger of Allah, peace and blessings of Allah be upon him, by which he would swear was, "No, and by the Turner of hearts."