Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) reports this from the Prophet (peace and blessings be upon him); he (peace and blessings be upon him) said: "Indeed the womb (that is, kinship) clings to the Most Merciful. The Most Merciful joins whoever joins it, and the Most Merciful cuts off whoever cuts it (kinship) off."
Ahmad and al-Bazzar recorded it, and al-Tabarani recorded something similar; its chain contains a narrator, Salih the freedman of al-Taw'amah, who suffered from confusion (ikhtilat); the rest of its narrators are the narrators of the Sahih.