Ruth 4:4, 8

So I thought to let you hear of it, saying, ‘Buy it in the presence of those sitting here, and before the elders of my people. If you will redeem it, redeem it; but if not, then tell me, so that I may know; for there is no one besides you to redeem it, and I am [next of kin] after you.’ ” And he said, “I will redeem it.”

So, when the closest relative (redeemer) said to Boaz, “Buy it for yourself,” he pulled off his sandal [and gave it to Boaz to confirm the agreement].