Ruth 4:5

Observe the action of the Levirate law. If there had been no one interested but Naomi, she would have sold the land unclogged by any condition, the law of Levirate having no existence in her case. But there was a young widow upon whom the possession of the land would devolve at Naomi’s death, and who already had a right of partnership in it, and the law of Levirate did apply in her case. It was, therefore, the duty of the גאל gā'al to marry her and raise up seed to his brother, i. e. his kinsman. And he could not exercise his right of redeeming the land, unless he was willing at the same time to fulfill his obligations to the deceased by marrying the widow. This he was unwilling to do.