Deuteronomy 25:5
5 "If two brothers are living together on the same property and one of them dies without a son, his widow may not be married to anyone from outside the family. Instead, her husband's brother should marry her and have intercourse with her to fulfill the duties of a brother-in-law.
Holy Bible. New Living Translation copyright© 1996, 2004, 2007, 2013 by Tyndale House Foundation. Used by permission of Tyndale House Publishers Inc., Carol Stream, Illinois 60188. All rights reserved.
Matthew Henry's Commentary on Deuteronomy 25:5
Commentary on Deuteronomy 25:5-12
(Read Deuteronomy 25:5-12)
The custom here regulated seems to have been in the Jewish law in order to keep inheritances distinct; now it is unlawful.