It was narrated that Ibn 'Umar said: The Messenger of Allah said: 'Whoever swears, let him not swear by anything other than Allah.' The Quraish used to swear by their forefathers, and so he said: Do not swear by your forefathers.
Yahya bin Abi Ishaq said: A man from Banu Ghifar told me, in the gathering of Salim bin 'Abdullah, Salim bin 'Abdullah said: 'I heard 'Abdullah -that is, Ibn 'Umar- say: The Messenger of Allah said: 'Allah forbids you to swear by your forefathers.' '