When brothers dwell together and one of them dies without a son, the widow must not marry outside the family. Her husband's brother is to take her as his wife and fulfill the duty of a brother-in-law for her.

Matthew 22:24
"Teacher," they said, "Moses declared that if a man dies without having children, his brother is to marry the widow and raise up offspring for him.

Mark 12:19
"Teacher, Moses wrote for us that if a man's brother dies and leaves a wife but no children, the man is to marry his brother's widow and raise up offspring for him.

Luke 20:28
"Teacher," they said, "Moses wrote for us that if a man's brother dies and leaves a wife but no children, the man is to marry his brother's widow and raise up offspring for him.

Genesis 19:31
One day the older daughter said to the younger, "Our father is old, and there is no man in the land to sleep with us, as is the custom over all the earth.

Genesis 38:8
Then Judah said to Onan, "Sleep with your brother's wife. Perform your duty as her brother-in-law and raise up offspring for your brother."

Ruth 1:11
But Naomi replied, "Return home, my daughters. Why would you go with me? Are there still sons in my womb to become your husbands?

Ruth 3:2
Now is not Boaz, with whose servant girls you have been working, a relative of ours? In fact, tonight he is winnowing barley on the threshing floor.

Ruth 3:13
Stay here tonight, and in the morning, if he wants to redeem you, good. Let him redeem you. But if he does not want to redeem you, as surely as the LORD lives, I will. Now lie here until morning."

Ruth 4:5
Then Boaz said, "On the day you buy the land from Naomi and also from Ruth the Moabitess, you must also acquire the widow of the deceased in order to raise up the name of the deceased on his inheritance."

If brothers dwell together, and one of them die, and have no child, the wife of the dead shall not marry without to a stranger: her husband's brother shall go in to her, and take her to him to wife, and perform the duty of an husband's brother to her.