Kabbalah zu Bereschit 27:21

Rabbi Elazar said, It was Jacob who sang this song, when his father said to him, "Come near, I pray you, that I may feel you, my son, whether you are really my son Esau or not" (Beresheet 27:21). Then was Jacob in great distress, for he feared that his father will recognize and know him. Then it is written, "and he recognized him not, because his hands were hairy, as his brother Esau's hands, so he blessed him" (Beresheet 27: 23). So he said, "In my distress I cried to Hashem, and He heard me."