פירוש על עבודה זרה 49:11

The first part of this quote is the same that we saw above—Sefer Hayashar is Genesis. Then the Talmud asks where the hint is in Genesis that the children of Judah should learn to use the bow. This they find in a creative reading of Jacob’s blessing in Genesis 49:8. Judah is told that his hands will be on the neck of your enemies. The midrash interprets this to mean not on the neck, but directed at their necks, with arrows.