Deuteronomy 25:4-8

“You shall not muzzle the ox while it is threshing.

“When brothers live together, and one of them dies and has no son, the wife of the deceased shall not be married outside the family to a strange man. Her husband’s brother shall have relations with her and take her to himself as his wife, and perform the duty of a husband’s brother to her.

It shall then be that the firstborn to whom she gives birth shall assume the name of his father’s deceased brother, so that his name will not be wiped out from Israel.

But if the man does not desire to take his brother’s widow, then his brother’s widow shall go up to the gate to the elders, and say, ‘My husband’s brother refuses to establish a name for his brother in Israel; he is not willing to perform the duty of a husband’s brother to me.’

Then the elders of his city shall summon him and speak to him. And if he persists and says, ‘I do not desire to take her,’