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.

Note Deuteronomy 25:5

BSB · Berean Standard Bible
Master, Moses wrote unto us, If a man’s brother die, and leave his wife behind him, and leave no children, that his brother should take his wife, and raise up seed unto his brother.
KJV · King James Version
“Teacher, Moses wrote to us, ‘If a man’s brother dies and leaves a wife behind him, and leaves no children, that his brother should take his wife and raise up offspring for his brother.’
WEB · World English Bible
Teacher, Moses wrote unto us, If a man’s brother die, and leave a wife behind him, and leave no child, that his brother should take his wife, and raise up seed unto his brother.
ASV · American Standard Version

Related passages

From the Treasury of Scripture Knowledge, grouped by the word they explain.

If
Genesis 38:8; Deuteronomy 25:5–10; Ruth 4:5
that
Ruth 1:11–13