Musnad Ahmad 27:340

Waki’ narrated to us, Sufyan narrated to us, from Musa—Waki’ said: We think it is Ibn ‘Uqbah—from Salim, from Ibn ‘Umar, who said: The oath of the Prophet, peace and blessings of Allah be upon him, by which he would swear was, "No, and by the Turner of hearts."