Musnad Ahmad 28:256

Ishaq ibn Isa narrated to us, Abd al-Rahman ibn Abi al-Zinad narrated to us, from Abd al-Rahman ibn al-Harith, from Amr ibn Shu'ayb, from his father, from his grandfather, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "There is no vow except in that by which the Face of Allah, the Almighty and Majestic, is sought. And there is no oath in severing ties of kinship."