Musnad Ahmad 10:5

Yazid ibn Harun narrated to us, Hisham al-Dastawa'i informed us, from Yahya ibn Abi Kathir, from Ibrahim ibn Abdullah ibn Qariz, that his father narrated to him: That he entered upon Abd al-Rahman ibn Awf while he was ill. Abd al-Rahman said to him: May your ties of kinship be joined, for the Prophet, peace and blessings of Allah be upon him, said: "Allah the Almighty said: 'I am the Most Merciful (al-Rahman). I created the womb (al-rahim), and I derived for it a name from My name. Whoever joins it, I join him, and whoever severs it, I sever him.' So he cuts it off—or he said: Whoever cuts it off, I cut him off."