Genesis 25:1

Again Abraham took a wife. Though Abraham’s loneliness following the death of Sarah had impressed upon him an awareness of his own advancing age (see on Genesis 24:1), he still enjoyed remarkable physical and mental strength and lived for 38 years after her death. Isaac’s marriage may have left Abraham even more lonely than before and led him to take another wife to make his last years happy ones. That this new wife, Keturah, meaning “incense,” is called a concubine, like Hagar (v. 6), does not imply that he had married her while Sarah was still alive, though this is not impossible. The context conveys the impression that Abraham’s marriage to Keturah occurred after Sarah’s death.