Musnad Ahmad 28:341

Waki’ narrated to us, Fitr narrated to us, and Yazid ibn Harun said: Fitr informed us, from Mujahid, from Abdullah ibn ‘Amr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the womb (kinship) is hanging from the Throne. The one who maintains ties is not the one who reciprocates, but rather the one who maintains ties is he who, when his kinship is severed, maintains it." Yazid said: The one who maintains ties.