Musnad Ahmad 28:48

Ya'la narrated to us, Fitr narrated to 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 suspended from the Throne. The one who maintains ties is not the one who reciprocates, but the one who maintains ties is he who, when his kinship is severed, maintains it."