Almost at the same time, when Abraham was now a hundred years old, his son Isaac was born. Then Sara expelled the maid-servant by whom Abraham had had a son; and she is said to have dwelt in the desert along with her son, and defended by the help of God. Not long after this, God tried the faith of Abraham, and required that his son Isaac should be sacrificed to him by his father. Abraham did not hesitate to offer him, and had already laid the lad upon the altar, and was drawing the sword to slay him, when a voice came from heaven commanding him to spare the young man; and a ram was found at hand to be for a victim.
When the sacrifice was offered, God spoke to Abraham, and promised him those things which he had already said he would bestow. But Sara died in her one hundred and twenty-seventh year, and her body was, through the care of her husband, buried in Hebron, a town of the Canaanites, for Abraham was staying in that place. Then Abraham, seeing that his son Isaac was now of youthful age, for he was, in fact, in his fortieth year, enjoined his servant to seek a wife for him, but only from that tribe and territory from which he himself was known to be descended.
He was instructed, however, on finding the girl, to bring her into the land of the Canaanites, and not to suppose that Isaac would return into the country of his father for the purpose of obtaining a wife. In order that the servant might carry out those instructions zealously, Abraham administered an oath to him, while his hand rested on the thigh of his master. The servant accordingly set out for Mesopotamia, and came to the town of Nachor, the brother of Abraham. He entered into the house of Bathuel, the Syrian, son of Nachor; and having seen Rebecca, a beautiful virgin, the daughter of Nachor, he asked for her, and brought her to his master.
After this, Abraham took a wife named Kethurah, who is called in the Chronicles his concubine, and begot children by her. But he left his possessions to Isaac, the son of Sara, while, at the same time, he distributed gifts to those whom he had begotten by his concubines; and thus they were separated from Isaac. Abraham died after a life of a hundred and seventy-five years; and his body was laid in the tomb of Sara his wife.
Source: Sacred History (New Advent)