"Some time later Abraham was told, 'Milkah is also a mother; she has borne sons to your brother Nahor:'" NIV translation
Abraham's brother Nahor was still living in Mesopotamia. Abraham received word that his brother had children and this would be important when it came time for his descendants to find wives.
"'Uz the firstborn, Buz his brother, Kemuel (the father of Aram), Kesed, Hazo, Pildash, Jidlaph and Bethuel. Bethuel became the father of Rebekah. Milkah bore these eight sons to Abraham's brother Nahor. His concubine, whose name was Reumah, also had sons: Tebah, Gaham, Tahash and Maakah.'" NIV translation
In all, Nahor had twelve sons. This seems to be a pattern in the lives of Abraham's family. Nahor's descendants would be known as the Aramean tribes. As we see it is from these tribes that Rebekah would come.