Deuteronomy 21:17

Instead, he must acknowledge the firstborn, the son of his unloved wife, by giving him a double portion of all that he has. For that son is the firstfruits of his father’s strength; the right of the firstborn belongs to him.
BSB · Berean Standard Bible
But he shall acknowledge the son of the hated for the firstborn, by giving him a double portion of all that he hath: for he is the beginning of his strength; the right of the firstborn is his.

Note that…: Heb. that is found with him

KJV · King James Version
but he shall acknowledge the firstborn, the son of the hated, by giving him a double portion of all that he has; for he is the beginning of his strength. The right of the firstborn is his.
WEB · World English Bible
but he shall acknowledge the first-born, the son of the hated, by giving him a double portion of all that he hath; for he is the beginning of his strength; the right of the first-born is his.
ASV · American Standard Version

Related passages

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

by giving
Genesis 25:5, 6, 32, 34; 1 Chronicles 5:1, 2
that he hath
Heb. that is found with him. the beginning.
Genesis 49:3; Psalm 105:36
the right
Genesis 25:31–34